Prevent USB activities if application instance is already running
Raise Settings window on top of windows stack after showing
Don't use C++11 due to Mac OS X 10.6.8 support

On OSX platform we have to use libstd++ as stdlib. If we use C++11
compiler generates code that links against libc++ regardless of qmake
options. So, get rid of C++11 while not-so-many modifications are
needed.