Fix for bug#35383: binlog playback and replication breaks

due to name_const substitution

Problem:
"In general, statements executed within a stored procedure
are written to the binary log using the same rules that
would apply were the statements to be executed in standalone
fashion. Some special care is taken when logging procedure
statements because statement execution within procedures
is not quite the same as in non-procedure context".

For example, each reference to a local variable in SP's
statements is replaced by NAME_CONST(var_name, var_value).
Queries like
"CREATE TABLE ... SELECT FUNC(local_var ..."
are logged as
"CREATE TABLE ... SELECT FUNC(NAME_CONST("local_var", var_value) ..."
that leads to differrent field names and
might result in "Incorrect column name" if var_value is long enough.

Fix: in 5.x we'll issue a warning in such a case.
In 6.0 we should get rid of NAME_CONST().

Note: this issue and change should be described in the documentation
("Binary Logging of Stored Programs").

sql/sql_class.h

@@ -1556,6 +1556,9 @@ public:
   sp_cache   *sp_proc_cache;
   sp_cache   *sp_func_cache;
 
+  /** number of name_const() substitutions, see sp_head.cc:subst_spvars() */
+  uint       query_name_consts;
+
   /*
     If we do a purge of binary logs, log index info of the threads
     that are currently reading it needs to be adjusted. To do that