Simplify some file list usage using filters new to QT4

QT4 introduced a 'QDir::NoDotAndDotDot' filter for use with QDir::setFilter(),
QDir::entryList() and QDir::entryInfoList(). This allows us to
simplify a few places in the code by removing our own . and .. checks.

Thanks to Rolf Eike Beer <eike@sf-mail.de> for spotting the problem
and providing an example patch. Since there were many more examples in
the code than the one he highlighted I decided to fix them all in one
commit instead of applying his patch.