liba52 is not always used for AC-3 decoding.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@14120 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

doc/general.texi

@@ -272,7 +272,7 @@ following image formats are supported:
 @item MPEG audio layer 1/3   @tab X   @tab  IX
 @tab MP3 encoding is supported through the external library LAME.
 @item AC-3                   @tab  IX  @tab  IX
-@tab liba52 is used internally for decoding.
+@tab liba52 can be used alternatively for decoding.
 @item Vorbis                 @tab  X   @tab  X
 @item WMA V1/V2              @tab X    @tab X
 @item AAC                    @tab X    @tab X