Rockbox Utility: use libmp3lame for voice clips.

Instead of calling the lame executable use libmp3lame directly. As result, this
simplifies the prerequisites for creating voice clips for Archos devices to
putting the library in the system's search path (Windows: put libmp3lame.dll in
the search path or the same folder RockboxUtility.exe is located in. Linux:
install the library using your systems package manager) and configuration.

This creates a notable encoding speedup on Windows (around factor 6 on my test
setup) and a small speedup on Linux (around factor 1.2).

The implemenatation currently has the following limitations:
- Only enabled on Windows and Linux. On OS X installing the correct dylib is a
  bit nontrivial, so using the old command line based method is still in use
  for now.
- The encoder parameters are currently hardcoded to use the same values the
  build system uses.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@31634 a1c6a512-1295-4272-9138-f99709370657

rbutil/rbutilqt/base/encoderbase.cpp

@@ -20,6 +20,7 @@
 #include "utils.h"
 #include "rbsettings.h"
 #include "encoderrbspeex.h"
+#include "encoderlame.h"
 #include "encoderexe.h"
 
 /*********************************************************************
@@ -55,7 +56,12 @@ EncoderBase* EncoderBase::getEncoder(QObject* parent,QString encoder)
     EncoderBase* enc;
     if(encoder == "lame")
     {
+#if defined(Q_OS_MACX)
+        /* currently not on OS X */
         enc = new EncoderExe(encoder,parent);
+#else
+        enc = new EncoderLame(parent);
+#endif
         return enc;
     }
     else  // rbspeex is default