Fix for bug #6849 "Crash while preparing query containing const expr with

IN and CONVERT_TZ()" (with after review changes).

Now we add implicitly used time zone tables to global table list right
at the parsing stage instead of doing it later in mysql_execute_command()
or in check_prepared_statement().

No special test-case needed since this bug also manifests itself as
timezone2.test failure if one runs it with --ps-protocol option.


sql/sql_base.cc:
  relink_tables_for_multidelete(): 
   presence of implicitly used time zone tables is no longer condition for
   propagation of TABLE pointers from global table list to local table
   lists (since now global list is always created...)
sql/sql_lex.cc:
  - Added LEX::add_time_zone_tables_to_query_tables() function which adds
    implicitly used time zone tables to global table list.
  - Definition of fake_time_zone_tables_list moved to tztime.cc, since
    it is no longer used in parser.
sql/sql_lex.h:
  - Since now we add implicitly used time zone tables right at parsing
    stage, LEX::time_zone_tables_used is either zero or points to valid
    time zone tables list. Updated its description to reflect that.
  - Added LEX::add_time_zone_tables_to_query_tables() function which adds
    implicitly used time zone tables to global table list.
  - Declaration of fake_time_zone_tables_list moved to tztime.h,
    since it is no longer used in parser.
sql/sql_parse.cc:
  mysql_execute_command():
    Removed adding list of implicitly used time zone tables to global table
    list, since now we do this right at the parsing stage.
sql/sql_yacc.yy:
  Let us add implicitly used time zone tables to global table list
  right at the parsing stage instead of doing it later in
  mysql_execute_command() or in check_prepared_statement().
sql/tztime.cc:
  Moved fake_time_zone_tables_list definition from sql_lex.cc to
  tztime.cc since now it is used only for error reporting from
  my_tz_get_table_list() function.
sql/tztime.h:
  Moved fake_time_zone_tables_list declaration from sql_lex.h to
  tztime.h since now it is used only for error reporting from
  my_tz_get_table_list() function.

sql/tztime.h

@@ -64,6 +64,7 @@ extern Time_zone * my_tz_find(const String *name, TABLE_LIST *tz_tables);
 extern my_bool     my_tz_init(THD *org_thd, const char *default_tzname, my_bool bootstrap);
 extern void        my_tz_free();
 
+extern TABLE_LIST fake_time_zone_tables_list;
 
 /*
   Check if we have pointer to the beggining of list of implictly used