Replace the source of gsm with the standard library

After intalling the libraries libgsm1 and libgsm1-dev, you can create the shared library codec_gsm.so with:
gcc -shared -o codec_gsm.so gsmcodec.cpp -lgsm

doc/Dependencies.txt

@@ -18,6 +18,7 @@ libsamplerate        0.1.2      http://www.mega-nerd.com/SRC/[website]
 libdbus-glib         0.73       Packaged with your favorite distribution.
 dbus-c++-1           0.5        See Build notes.
 libexpat1            1.95.8     Packaged with your favorite distribution.
+libgsm1		     1.0.10     Ubuntu package - Necessary to use GSM codec.
 --------------------------------------------------------------------------------------
 
 

src/audio/gsmcodec.cpp

@@ -30,7 +30,7 @@ public:
 Gsm(int payload = 0) 
 : AudioCodec(payload, "GSM")
 {
-  _description = "GSM";
+  //_description = "GSM";
   _clockRate = 8000;
   _channel   = 1;
   
@@ -72,7 +72,7 @@ private:
 
 // the class factories
 extern "C" AudioCodec* create() {
-    return new Gsm();
+    return new Gsm(3);
 }
 
 extern "C" void destroy(AudioCodec* a) {