fixed linking query_prealloc_size to query cache presence


mysql-test/r/query_cache.result:
  test of QC invalidation by LOCK command
mysql-test/t/query_cache.test:
  test of QC invalidation by LOCK command
sql/mysqld.cc:
  new variable query_cache_wlock_invalidate
  fixed query_prealloc_size with QC absence
sql/set_var.cc:
  new variable query_cache_wlock_invalidate
sql/sql_cache.cc:
  new method for table invalidation
sql/sql_cache.h:
  new method for table invalidation
sql/sql_class.h:
  new variable query_cache_wlock_invalidate
sql/sql_parse.cc:
  layout fixed