A bit of harmless refactoring

Prefer C++-style over C-style type casting.
Use qApp instead of QApplication/QCoreApplication::instance().
Use explicit QString::fromLatin1()/fromUtf8() where applicable.


git-svn-id: file:///data/workdir/Transmission-svn/trunk@14404 1bcf1a7e-6170-4b50-b784-84ec52b2dec6