Fixed sql for user profile installation.

Escape "key" with backquote to be compatible with MySQL.

modules/core/site/scripts/user_profile.sql

@@ -2,5 +2,5 @@ CREATE TABLE user_profiles(
   `uid` INTEGER NOT NULL CHECK("uid">=0),
   `key` VARCHAR(255) NOT NULL,
   `value` TEXT,
-  CONSTRAINT PK_uid_key PRIMARY KEY (uid,key)
+  CONSTRAINT PK_uid_key PRIMARY KEY (`uid`,`key`)
 );