Code cleanup to get fewer reallocs() during execution.

- Changed TABLE->alias to String to get fewer reallocs when alias are used.
- Preallocate some buffers

Changed some String->c_ptr() -> String->ptr() when \0 is not needed.
Fixed wrong usage of String->ptr() when we need a \0 terminated string.
Use my_strtod() instead of my_atof() to avoid having to add \0 to string.
c_ptr() -> c_ptr_safe() to avoid warnings from valgrind.
zr 

sql/event_db_repository.cc:
  Update usage of TABLE->alias
sql/event_scheduler.cc:
  c_ptr() -> c_ptr_safe()
sql/events.cc:
  c_ptr() -> ptr() as \0 was not needed
sql/field.cc:
  Update usage of TABLE->alias
sql/field.h:
  Update usage of TABLE->alias
sql/ha_partition.cc:
  Update usage of TABLE->alias
sql/handler.cc:
  Update usage of TABLE->alias
  Fixed wrong usage of str.ptr()
sql/item.cc:
  Fixed error where code wrongly assumed string was \0 terminated.
sql/item_func.cc:
  c_ptr() -> c_ptr_safe()
  Update usage of TABLE->alias
sql/item_sum.h:
  Use my_strtod() instead of my_atof() to avoid having to add \0 to string
sql/lock.cc:
  Update usage of TABLE->alias
sql/log.cc:
  c_ptr() -> ptr() as \0 was not needed
sql/log_event.cc:
  c_ptr_quick() -> ptr() as \0 was not needed
sql/opt_range.cc:
  ptr() -> c_ptr() as \0 is needed
sql/opt_subselect.cc:
  Update usage of TABLE->alias
sql/opt_table_elimination.cc:
  Update usage of TABLE->alias
sql/set_var.cc:
  ptr() -> c_ptr() as \0 is needed
  c_ptr() -> c_ptr_safe()
sql/sp.cc:
  c_ptr() -> ptr() as \0 was not needed
sql/sp_rcontext.cc:
  
  Update usage of TABLE->alias
sql/sql_base.cc:
  Preallocate buffers
  Update usage of TABLE->alias
sql/sql_class.cc:
  Fix arguments to sprintf() to work even if string is not \0 terminated
sql/sql_insert.cc:
  Update usage of TABLE->alias
  c_ptr() -> ptr() as \0 was not needed
sql/sql_load.cc:
  Preallocate buffers
  Trivial optimizations
sql/sql_parse.cc:
  Trivial optimization
sql/sql_plugin.cc:
  c_ptr() -> ptr() as \0 was not needed
sql/sql_select.cc:
  Update usage of TABLE->alias
sql/sql_show.cc:
  Update usage of TABLE->alias
sql/sql_string.h:
  Added move() function to move allocated memory from one object to another.
sql/sql_table.cc:
  Update usage of TABLE->alias
  c_ptr() -> c_ptr_safe()
sql/sql_test.cc:
  ptr() -> c_ptr_safe()
sql/sql_trigger.cc:
  Update usage of TABLE->alias
  c_ptr() -> c_ptr_safe()
sql/sql_update.cc:
  Update usage of TABLE->alias
sql/sql_view.cc:
  ptr() -> c_ptr_safe()
sql/sql_yacc.yy:
  ptr() -> c_ptr()
sql/table.cc:
  
  Update usage of TABLE->alias
sql/table.h:
  Changed TABLE->alias to String to get fewer reallocs when alias are used.
storage/federatedx/ha_federatedx.cc:
  Use c_ptr_safe() to ensure strings are \0 terminated.
storage/maria/ha_maria.cc:
  Update usage of TABLE->alias
storage/myisam/ha_myisam.cc:
  Update usage of TABLE->alias
storage/xtradb/row/row0sel.c:
  Ensure that null bits in record are properly reset.
  (Old code didn't work as row_search_for_mysql() can be called twice while reading fields from one row.

sql/sql_table.cc

@@ -2113,7 +2113,7 @@ int mysql_rm_table_part2(THD *thd, TABLE_LIST *tables, bool if_exists,
   {
     if (!foreign_key_error)
       my_printf_error(ER_BAD_TABLE_ERROR, ER(ER_BAD_TABLE_ERROR), MYF(0),
-                      wrong_tables.c_ptr());
+                      wrong_tables.c_ptr_safe());
     else
       my_message(ER_ROW_IS_REFERENCED, ER(ER_ROW_IS_REFERENCED), MYF(0));
     error= 1;
@@ -6955,7 +6955,7 @@ view_err:
       error= 0;
       push_warning_printf(thd, MYSQL_ERROR::WARN_LEVEL_NOTE,
 			  ER_ILLEGAL_HA, ER(ER_ILLEGAL_HA),
-			  table->alias);
+			  table->alias.c_ptr());
     }
 
     VOID(pthread_mutex_lock(&LOCK_open));
@@ -7023,7 +7023,7 @@ view_err:
       error= 0;
       push_warning_printf(thd, MYSQL_ERROR::WARN_LEVEL_NOTE,
 			  ER_ILLEGAL_HA, ER(ER_ILLEGAL_HA),
-			  table->alias);
+			  table->alias.c_ptr());
     }
 
     if (!error)