Prevents incorrect table aliases

When one uses a discriminator map with a valid, but incorrectly cased,
class name (Foo\\Bar\\baz instead of Foo\\Bar\\baz) for instance, the
class metadata won't complain (php being case insensitive when it comes
to class name). However, it will complain if the class does not exist.

This will lead to "exotic" table alias being generated when querying the
parent class because the sqlTableAliases won't contain the wrongly typed
classname.

Example:

SELECT t0.id as id_0, ..., t1.name as name_10, t11.thing as thing_11...

lib/Doctrine/ORM/Persisters/Entity/BasicEntityPersister.php

@@ -1605,13 +1605,13 @@ protected function getSQLTableAlias($tableName, $assocName = '')
             $tableName .= '#' . $assocName;
         }
 
-        if (isset($this->currentPersisterContext->sqlTableAliases[$tableName])) {
-            return $this->currentPersisterContext->sqlTableAliases[$tableName];
+        if (isset($this->currentPersisterContext->sqlTableAliases[strtolower($tableName)])) {
+            return $this->currentPersisterContext->sqlTableAliases[strtolower($tableName)];
         }
 
         $tableAlias = 't' . $this->currentPersisterContext->sqlAliasCounter++;
 
-        $this->currentPersisterContext->sqlTableAliases[$tableName] = $tableAlias;
+        $this->currentPersisterContext->sqlTableAliases[strtolower($tableName)] = $tableAlias;
 
         return $tableAlias;
     }