mod.c: new demux2 for MOD files using libmodplug library.

 (modplug-xmms.sourceforge.net/)

 The demuxer is selected by extention look up.(mod, s3m, xm, it, 669,
amf, ams, dbm, dmf, dsm, far, mdl, med, mtm, okt, ptm, stm, ult, umx,
mt2, psm), I hope that won't give problems.

modules/demux/Modules.am

@@ -17,3 +17,4 @@ SOURCES_real = real.c
 SOURCES_ts2 = ts.c
 SOURCES_ps2 = ps.c
 SOURCES_dvdnav = dvdnav.c
+SOURCES_mod = mod.c