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.)

innobase/dict/dict0dict.c

@@ -3554,7 +3554,7 @@ dict_foreign_parse_drop_constraints(
 
 	ptr = dict_accept(ptr, "FOREIGN", &success);
 	
-	if (!success) {
+	if (!success || !ib_isspace(*ptr)) {
 
 	        goto loop;
 	}

mysql-test/r/innodb_bug35220.result

+SET storage_engine=InnoDB;

mysql-test/t/innodb_bug35220.test

+#
+# Bug#35220 ALTER TABLE too picky on reserved word "foreign"
+# http://bugs.mysql.com/35220
+#
+
+-- source include/have_innodb.inc
+
+SET storage_engine=InnoDB;
+
+# we care only that the following SQL commands do not produce errors
+-- disable_query_log
+-- disable_result_log
+
+CREATE TABLE bug35220 (foreign_col INT, dummy_cant_delete_all_columns INT);
+ALTER TABLE bug35220 DROP foreign_col;
+DROP TABLE bug35220;