Trims whitespace from file so that install sql doesn't fail on some servers

Tracker item http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=33154

The installation of extensions, with manifest file formatted as follows, will fail due to the white space in the file name. This PR trims that white space to resolve the failure.

```
<install>
	<sql>
		<file driver="mysql"
		      charset="utf8">sql/install.mysql.utf8.sql
		</file>
	</sql>
</install>
```