Added multiple track export feature.

Here is the patchset for my multiple track export feature. It works now
the way I originally envisioned.

For example, after I export tracks on my little song, I see this in the
directory I created:

devin@devin-studio:~/lmms/projects/fff$ ls
0_Defaultpreset.wav  3_Defaultpreset.wav      6_csidSouwav.wav
1_Defaultpreset.wav  4_spacenoiseswavwav.wav  7_HHOPENwav.wav
2_Defaultpreset.wav  5_csidkickwav.wav        8_HHOPENwav.wav

Each instrument or sample track is exported individually, regardless of
whether in its own song track or playing as part of a BB track. The
name is taken from either the song track name or from the BB track name.
My goal was to get the tracks individually exported, so that I could
combine them with other tracks in Ardour.

Signed-off-by: Tobias Doerffel <tobias.doerffel@gmail.com>

src/core/ProjectRenderer.cpp

@@ -35,7 +35,7 @@
 #ifdef LMMS_HAVE_SCHED_H
 #include <sched.h>
 #endif
-
+#include <QMutexLocker>
 
 FileEncodeDevice __fileEncodeDevices[] =
 {
@@ -126,6 +126,7 @@ ProjectRenderer::ExportFileFormats ProjectRenderer::getFileFormatFromExtension(
 
 void ProjectRenderer::startProcessing()
 {
+
 	if( isReady() )
 	{
 		// have to do mixer stuff with GUI-thread-affinity in order to
@@ -139,11 +140,11 @@ void ProjectRenderer::startProcessing()
 			QThread::HighPriority
 #endif
 						);
+
 	}
 }
 
 
-
 void ProjectRenderer::run()
 {
 #if 0
@@ -157,6 +158,7 @@ void ProjectRenderer::run()
 #endif
 #endif
 
+
 	engine::getSong()->startExport();
 
 	song::playPos & pp = engine::getSong()->getPlayPos(