Cherry-pick fix for Bug#35220 from innodb-5.0-ss2475 snapshot.

Bug#35220: ALTER TABLE too picky on reserved word "foreign"

In ALTER TABLE, change the internal parser to search for
``FOREIGN[[:space:]]'' instead of only ``FOREIGN'' when parsing
ALTER TABLE ... DROP FOREIGN KEY ...; otherwise it could be mistaken
with ALTER TABLE ... DROP foreign_col;

(This fix is already present in MySQL 5.1 and higher.)

mysql-test/r/innodb_bug35220.result

@@ -0,0 +1 @@
+SET storage_engine=InnoDB;