Commit of some improvements when running under Cygwin

* musredit can now be built using Qt 4.5.3 of Cygwin 1.7---however, without online help
* FFTW3 threading in some user functions has been disabled

Obviously, there is a major problem when running musrgui/musredit with Cygwin on Windows7/64bit.
This has not been solved by this commit!

src/musredit/PGetPlotBlockDialog.cpp

@@ -162,8 +162,12 @@ void PGetPlotBlockDialog::helpContent()
   if (fHelpUrl.isEmpty()) {
     QMessageBox::information(this, "**INFO**", "Will eventually show a help window");
   } else {
+    #ifdef _WIN32GCC
+    QMessageBox::information(this, "**INFO**", "If a newer Qt version was available, a help window would be shown!");
+    #else
     PHelp *help = new PHelp(fHelpUrl);
     help->show();
+    #endif // _WIN32GCC
   }
 }