Implemented MDEV-3941: CREATE TABLE xxx IF NOT EXISTS should not block if table exists.

- Added option to check_if_table_exists() to quickly check if table exists (either SHARE or .FRM)
- Extended lock_table_names() to not wait for meta data locks if CREATE IF NOT EXISTS is used.

mysql-test/r/create.result:
  New test case
mysql-test/t/create.test:
  New test case
sql/sql_base.cc:
  Added option to check_if_table_exists() to quickly check if table exists (either SHARE or .FRM)
  Extended lock_table_names() to not wait for meta data locks if CREATE IF NOT EXISTS is used.
sql/sql_base.h:
  Updated prototype
sql/sql_db.cc:
  Added extra argument to call to check_if_table_exists()

1 files changed, 2 insertions, 1 deletions

diff --git a/sql/sql_base.h b/sql/sql_base.h
index 6ec998c44f8..45d41777fea 100644
--- a/sql/sql_base.h
+++ b/sql/sql_base.h
@@ -302,7 +302,8 @@ TABLE *find_table_for_mdl_upgrade(THD *thd, const char *db,
                                   const char *table_name,
                                   bool no_error);
 void mark_tmp_table_for_reuse(TABLE *table);
-bool check_if_table_exists(THD *thd, TABLE_LIST *table, bool *exists);
+bool check_if_table_exists(THD *thd, TABLE_LIST *table, bool fast_check,
+                           bool *exists);
 int update_virtual_fields(THD *thd, TABLE *table,
       enum enum_vcol_update_mode vcol_update_mode= VCOL_UPDATE_FOR_READ);
 int dynamic_column_error_message(enum_dyncol_func_result rc);