Use appnope in qt and wx gui support from the terminal; closes #6189

On Mavericks, the qt and wx gui support was unusable from the
ipython console in a terminal.  Using nope() in enable_qt4 and
enable_wx, and reversing with nap() in disable_qt4 and disable_wx,
solves the problem.
Merge pull request #6321 from efiring/fix_nap_qt_wx

Use appnope in qt and wx gui support from the terminal; closes #6189