Update for new style guidelines regarding TABs and trailing whitespace.

Originally committed as revision 4908 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/ffmpeg-doc.texi

@@ -1143,8 +1143,11 @@ mixing statements and declarations;
 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
 @end itemize
 
-Indent size is 4. The TAB character should not be used.
+Indent size is 4.
 The presentation is the one specified by 'indent -i4 -kr'.
+The TAB character is forbidden outside of Makefiles as is any
+form of trailing whitespace. Commits containing either will be
+rejected by the CVS repository.
 
 Main priority in FFmpeg is simplicity and small code size (=less
 bugs).