Reduce usage of strlen()

Changes:
- To detect automatic strlen() I removed the methods in String that
  uses 'const char *' without a length:
  - String::append(const char*)
  - Binary_string(const char *str)
  - String(const char *str, CHARSET_INFO *cs)
  - append_for_single_quote(const char *)
  All usage of append(const char*) is changed to either use
  String::append(char), String::append(const char*, size_t length) or
  String::append(LEX_CSTRING)
- Added STRING_WITH_LEN() around constant string arguments to
  String::append()
- Added overflow argument to escape_string_for_mysql() and
  escape_quotes_for_mysql() instead of returning (size_t) -1 on overflow.
  This was needed as most usage of the above functions never tested the
  result for -1 and would have given wrong results or crashes in case
  of overflows.
- Added Item_func_or_sum::func_name_cstring(), which returns LEX_CSTRING.
  Changed all Item_func::func_name()'s to func_name_cstring()'s.
  The old Item_func_or_sum::func_name() is now an inline function that
  returns func_name_cstring().str.
- Changed Item::mode_name() and Item::func_name_ext() to return
  LEX_CSTRING.
- Changed for some functions the name argument from const char * to
  to const LEX_CSTRING &:
  - Item::Item_func_fix_attributes()
  - Item::check_type_...()
  - Type_std_attributes::agg_item_collations()
  - Type_std_attributes::agg_item_set_converter()
  - Type_std_attributes::agg_arg_charsets...()
  - Type_handler_hybrid_field_type::aggregate_for_result()
  - Type_handler_geometry::check_type_geom_or_binary()
  - Type_handler::Item_func_or_sum_illegal_param()
  - Predicant_to_list_comparator::add_value_skip_null()
  - Predicant_to_list_comparator::add_value()
  - cmp_item_row::prepare_comparators()
  - cmp_item_row::aggregate_row_elements_for_comparison()
  - Cursor_ref::print_func()
- Removes String_space() as it was only used in one cases and that
  could be simplified to not use String_space(), thanks to the fixed
  my_vsnprintf().
- Added some const LEX_CSTRING's for common strings:
  - NULL_clex_str, DATA_clex_str, INDEX_clex_str.
- Changed primary_key_name to a LEX_CSTRING
- Renamed String::set_quick() to String::set_buffer_if_not_allocated() to
  clarify what the function really does.
- Rename of protocol function:
  bool store(const char *from, CHARSET_INFO *cs) to
  bool store_string_or_null(const char *from, CHARSET_INFO *cs).
  This was done to both clarify the difference between this 'store' function
  and also to make it easier to find unoptimal usage of store() calls.
- Added Protocol::store(const LEX_CSTRING*, CHARSET_INFO*)
- Changed some 'const char*' arrays to instead be of type LEX_CSTRING.
- class Item_func_units now used LEX_CSTRING for name.

Other things:
- Fixed a bug in mysql.cc:construct_prompt() where a wrong escape character
  in the prompt would cause some part of the prompt to be duplicated.
- Fixed a lot of instances where the length of the argument to
  append is known or easily obtain but was not used.
- Removed some not needed 'virtual' definition for functions that was
  inherited from the parent. I added override to these.
- Fixed Ordered_key::print() to preallocate needed buffer. Old code could
  case memory overruns.
- Simplified some loops when adding char * to a String with delimiters.

sql/sql_test.cc

@@ -127,25 +127,26 @@ void TEST_filesort(SORT_FIELD *sortorder,uint s_length)
   char buff[256],buff2[256];
   String str(buff,sizeof(buff),system_charset_info);
   String out(buff2,sizeof(buff2),system_charset_info);
-  const char *sep;
+  DBUG_ASSERT(s_length > 0);
   DBUG_ENTER("TEST_filesort");
 
   out.length(0);
-  for (sep=""; s_length-- ; sortorder++, sep=" ")
+  for (; s_length-- ; sortorder++)
   {
-    out.append(sep);
     if (sortorder->reverse)
       out.append('-');
     if (sortorder->field)
     {
       if (sortorder->field->table_name)
       {
-	out.append(*sortorder->field->table_name);
+        const char *table_name= *sortorder->field->table_name;
+	out.append(table_name, strlen(table_name));
 	out.append('.');
       }
-      out.append(sortorder->field->field_name.str ?
-                 sortorder->field->field_name.str :
-		 "tmp_table_column");
+      const char *name= sortorder->field->field_name.str;
+      if (!name)
+        name= "tmp_table_column";
+      out.append(name, strlen(name));
     }
     else
     {
@@ -153,7 +154,9 @@ void TEST_filesort(SORT_FIELD *sortorder,uint s_length)
       sortorder->item->print(&str, QT_ORDINARY);
       out.append(str);
     }
+    out.append(' ');
   }
+  out.chop();                                  // Remove last space
   DBUG_LOCK_FILE;
   (void) fputs("\nInfo about FILESORT\n",DBUG_FILE);
   fprintf(DBUG_FILE,"Sortorder: %s\n",out.c_ptr_safe());
@@ -186,8 +189,9 @@ TEST_join(JOIN *join)
       JOIN_TAB *tab= jt_range->start + i;
       for (ref= 0; ref < tab->ref.key_parts; ref++)
       {
-        ref_key_parts[i].append(tab->ref.items[ref]->full_name());
-        ref_key_parts[i].append("  ");
+        const char *full_name=(tab->ref.items[ref]->full_name());
+        ref_key_parts[i].append(full_name, strlen(full_name));
+        ref_key_parts[i].append(STRING_WITH_LEN("  "));
       }
     }