Change the AC-3 encoder to use floating-point.

Fixed-point AC-3 encoder renamed to ac3_fixed.
Regression test acodec-ac3 renamed to acodec-ac3_fixed.
Regression test lavf-rm changed to use ac3_fixed encoder.

Originally committed as revision 26209 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/allcodecs.c

@@ -222,6 +222,7 @@ void avcodec_register_all(void)
     REGISTER_ENCDEC  (AAC, aac);
     REGISTER_DECODER (AAC_LATM, aac_latm);
     REGISTER_ENCDEC  (AC3, ac3);
+    REGISTER_ENCODER (AC3_FIXED, ac3_fixed);
     REGISTER_ENCDEC  (ALAC, alac);
     REGISTER_DECODER (ALS, als);
     REGISTER_DECODER (AMRNB, amrnb);