fix relative paths with .. in wildcards

The absolute file paths that are returned by wildcards must not contain
substrings like "..". Running those through QDir::cleanPath now.
Autotest TestLanguage::wildcards enhanced.

Task-number: QBS-287

Change-Id: Id6882d9d6eaa875bed42ac1830afef43a705b4da
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>