Bitcoin-Qt: fix copy via context-menu broken

- as QClipboard::Selection isn't available on Windows ensure that the
  correct mode is called, but sill allow selection for e.g. X11
- start conversion from QCoreApplication::instance() to qApp in
  guiutil.cpp (I intend to harmonize this all over the source with my Qt5
  compatibility pull)
translation base files update 2013-04-02

- also includes a small change to a string in bitcoinrpc.cpp, which is not
  on Transifex anyway, so is safe to merge
Merge pull request #2446 from Diapolo/translations

translation base files update 2013-04-02
Merge pull request #2441 from Diapolo/Qt_fix_copy_context_menu

Bitcoin-Qt: fix copy via context-menu broken