Fix for remaining issues described in Bug #1664

"mysql_send_long_data() API call is completely broken".

Now we are resetting some members (long_data_supplied/null_value...) of Item_param to its 
initial state after each execution of prepared statement. We also manipulating 
Item_param::maybe_null/null_value only via Item_param::set_* setters which makes code a bit 
more robust.


sql/item.cc:
  Now we are assuming that Item_param may be NULL until we know this fact exactly.
  Added non-empty implementation of Item_param::reset() method which should be used
  for restoring Item_param state after each statment execution. (We need to clear 
  long_data_supplied flag, we also clear some other Item_param members here since it
  makes code simpler.)
sql/item.h:
  Now Item_param::reset() method really does something.
sql/sql_prepare.cc:
  Now we are calling Item_param::reset() for each parameter after execution for resetting Item_param
  to initial state. So we no longer don't need Prepared_statement::long_data_flag. We also 
  set Item_param::null_value/maybe_null value in Item_param::set_* and reset() methods 
  instead of doing it explicitly in insert_params_* functions (this by the way lowers 
  probability that we will forget to update one of such functions).
tests/client_test.c:
  Added test for Bug#1664 "mysql_send_long_data() API call is broken".

sql/sql_prepare.cc

@@ -91,7 +91,6 @@ public:
   uint last_errno;
   char last_error[MYSQL_ERRMSG_SIZE];
   bool get_longdata_error;
-  bool long_data_used;
   bool log_full_query;
 #ifndef EMBEDDED_LIBRARY
   bool (*set_params)(Prepared_statement *st, uchar *data, uchar *data_end,
@@ -465,12 +464,11 @@ static bool insert_params_withlog(Prepared_statement *stmt, uchar *null_array,
     {
       if (is_param_null(null_array, it - begin))
       {
-        param->maybe_null= param->null_value= param->value_is_set= 1;
+        param->set_null();
         res= &my_null_string;
       }
       else
       {
-        param->maybe_null= param->null_value= 0;
         if (read_pos >= data_end)
           DBUG_RETURN(1);
         param->set_param_func(param, &read_pos, data_end - read_pos);
@@ -503,10 +501,9 @@ static bool insert_params(Prepared_statement *stmt, uchar *null_array,
     if (!param->long_data_supplied)
     {
       if (is_param_null(null_array, it - begin))
-        param->maybe_null= param->null_value= param->value_is_set= 1;
+        param->set_null();
       else
       {
-        param->maybe_null= param->null_value= 0;
         if (read_pos >= data_end)
           DBUG_RETURN(1);
         param->set_param_func(param, &read_pos, data_end - read_pos);
@@ -562,11 +559,10 @@ static bool emb_insert_params(Prepared_statement *stmt)
     if (!param->long_data_supplied)
     {
       if (*client_param->is_null)
-        param->maybe_null= param->null_value= 1;
+        param->set_null();
       else
       {
 	uchar *buff= (uchar*)client_param->buffer;
-        param->maybe_null= param->null_value= 0;
         param->set_param_func(param, &buff,
                               client_param->length ? 
                               *client_param->length : 
@@ -604,13 +600,12 @@ static bool emb_insert_params_withlog(Prepared_statement *stmt)
     {
       if (*client_param->is_null)
       {
-        param->maybe_null= param->null_value= 1;
+        param->set_null();
         res= &my_null_string;
       }
       else
       {
 	uchar *buff= (uchar*)client_param->buffer;
-        param->maybe_null= param->null_value= 0;
         param->set_param_func(param, &buff,
                               client_param->length ? 
                               *client_param->length : 
@@ -1439,6 +1434,24 @@ static void reset_stmt_for_execute(Prepared_statement *stmt)
   }
 }
 
+
+/* 
+    Clears parameters from data left from previous execution or long data
+    
+  SYNOPSIS
+    reset_stmt_params()
+      stmt - prepared statement for which parameters should be reset
+*/
+
+static void reset_stmt_params(Prepared_statement *stmt)
+{
+  Item_param **item= stmt->param_array;
+  Item_param **end= item + stmt->param_count;
+  for (;item < end ; ++item)
+    (**item).reset();
+}
+
+
 /*
   Executes previously prepared query.
   If there is any parameters, then replace markers with the data supplied
@@ -1512,11 +1525,13 @@ void mysql_stmt_execute(THD *thd, char *packet, uint packet_length)
     my_pthread_setprio(pthread_self(), WAIT_PRIOR);
 
   cleanup_items(stmt->free_list);
+  reset_stmt_params(stmt);
   close_thread_tables(thd); // to close derived tables
   thd->set_statement(&thd->stmt_backup);
   DBUG_VOID_RETURN;
 
 set_params_data_err:
+  reset_stmt_params(stmt);
   thd->set_statement(&thd->stmt_backup);
   my_error(ER_WRONG_ARGUMENTS, MYF(0), "mysql_execute");
   send_error(thd);
@@ -1552,15 +1567,12 @@ void mysql_stmt_reset(THD *thd, char *packet)
 
   stmt->get_longdata_error= 0;
 
-  /* Free long data if used */
-  if (stmt->long_data_used)
-  {
-    Item_param **item= stmt->param_array;
-    Item_param **end= item + stmt->param_count;
-    stmt->long_data_used= 0;
-    for (; item < end ; item++)
-      (**item).reset();
-  }
+  /* 
+    Clear parameters from data which could be set by 
+    mysql_stmt_send_long_data() call.
+  */
+  reset_stmt_params(stmt);
+  
   DBUG_VOID_RETURN;
 }
 
@@ -1646,7 +1658,6 @@ void mysql_stmt_get_longdata(THD *thd, char *pos, ulong packet_length)
 #else
   param->set_longdata(thd->extra_data, thd->extra_length);
 #endif
-  stmt->long_data_used= 1;
   DBUG_VOID_RETURN;
 }
 
@@ -1658,7 +1669,6 @@ Prepared_statement::Prepared_statement(THD *thd_arg)
   param_count(0),
   last_errno(0),
   get_longdata_error(0),
-  long_data_used(0),
   log_full_query(0)
 {
   *last_error= '\0';