fts_query_t::nested_sub_exp: Keep track of nested
fts_ast_visit_sub_exp() calls.
fts_ast_visit_sub_exp(): Return DB_OUT_OF_MEMORY if the
maximum recursion depth is exceeded.
This is motivated by a change in MySQL 5.6.50:
mysql/mysql-server@e2a46b4834
Bug #29929684 USING MANY NESTED ARGUMENTS WITH BOOLEAN FTS CAN LEAD
TO TERMINATE SERVER
Problem:
=======
Multiple insert statement in table contains FULLTEXT KEY and a
FTS_DOC_ID column aborts the server if the FTS_DOC_ID exceeds
FTS_DOC_ID_MAX_STEP.
Solution:
========
Remove the exception for first committed insert statement.
Reviewed-by: Jimmy Yang<jimmy.yang@oracle.com>
RB: 18023
