mysql-test/r/query_cache.result:
  Added 5.0 testcase
mysql-test/t/query_cache.test:
  Added 5.0 test case
sql/mysql_priv.h:
  Added support for div_precision_increment
sql/set_var.cc:
  - Added query cache flush when system variable ft_boolean_syntax is
    updated since this also invalidates all cached result sets using this
    variable.
sql/sql_cache.cc:
  - Added the local system variable div_precision_increment as an identification flag
    for cached queries.