Fixed bug#36742 - GRANT hostname case handling inconsistent.

mysql-test/r/grant.result:
  It was added result for test case for bug#36742.
mysql-test/t/grant.test:
  It was added test case for bug#36742.
sql/sql_yacc.yy:
  It was added convertation of host name part of user name to lowercase.

mysql-test/r/grant.result

@@ -1429,3 +1429,14 @@ DROP USER 'testbug'@localhost;
 DROP TABLE db2.t1;
 DROP DATABASE db1;
 DROP DATABASE db2;
+#
+# Bug #36742
+#
+grant usage on Foo.* to myuser@Localhost identified by 'foo';
+grant select on Foo.* to myuser@localhost;
+select host,user from mysql.user where User='myuser';
+host	user
+localhost	myuser
+revoke select on Foo.* from myuser@localhost;
+delete from mysql.user where User='myuser';
+flush privileges;

mysql-test/t/grant.test

@@ -1550,5 +1550,15 @@ DROP TABLE db2.t1;
 DROP DATABASE db1;
 DROP DATABASE db2;
 
+--echo #
+--echo # Bug #36742
+--echo #
+grant usage on Foo.* to myuser@Localhost identified by 'foo';
+grant select on Foo.* to myuser@localhost;
+select host,user from mysql.user where User='myuser';
+revoke select on Foo.* from myuser@localhost;
+delete from mysql.user where User='myuser';
+flush privileges;
+
 # Wait till we reached the initial number of concurrent sessions
 --source include/wait_until_count_sessions.inc

sql/sql_yacc.yy

@@ -11567,6 +11567,12 @@ user:
                                          system_charset_info, 0) ||
                 check_host_name(&$$->host))
               MYSQL_YYABORT;
+            /*
+              Convert hostname part of username to lowercase.
+              It's OK to use in-place lowercase as long as
+              the character set is utf8.
+            */
+            my_casedn_str(system_charset_info, $$->host.str);
           }
         | CURRENT_USER optional_braces
           {