Made a start at implementing an option to use multi-threaded FFTs.

New command-line option for jt9: [-m nthreads].  Default is nthreads=1.
Also refactored a loop in filbig.f90 that was taking far too much
time.


git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@4916 ab8295b8-cf94-4d9e-aec4-7959e3be5d79

mainwindow.cpp

@@ -375,7 +375,8 @@ MainWindow::MainWindow(bool multiple, QSettings * settings, QSharedMemory *shdme
 
   QStringList jt9_args {
     "-s", QApplication::applicationName ()
-      , "-w", "1"
+        , "-w", "1"                                     //FFTW patience
+        , "-m", "1"                                     //FFTW threads
       , "-e", QDir::toNativeSeparators (m_appDir)
       , "-a", QDir::toNativeSeparators (m_dataDir.absolutePath ())
       , "-t", QDir::toNativeSeparators (m_config.temp_dir ().absolutePath ())