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, 1 insertions, 1 deletions

diff --git a/sql/sql_db.cc b/sql/sql_db.cc
index 5704b6d51b6..99e5f3a035c 100644
--- a/sql/sql_db.cc
+++ b/sql/sql_db.cc
@@ -927,7 +927,7 @@ update_binlog:
       char quoted_name[FN_REFLEN+3];
 
       // Only write drop table to the binlog for tables that no longer exist.
-      if (check_if_table_exists(thd, tbl, &exists))
+      if (check_if_table_exists(thd, tbl, 0, &exists))
       {
         error= true;
         goto exit;