fix support of audio channel mixers, like the headphone channel mixer
for instance, which was broken since the introduction of user audio
filters; if specified by the user and compatible with the audio
pipeline, we add the channel mixer after the user filters.
-> unfortunately, this fix removed two strings and introduced 4 new
ones
-> TODO: allow the user to choose only amongst channel mixers, not
all available audio filters
* vlc.exe.manifest Makefile.am install-win32 :
add a manifest file to allow the win32 gui to use Windows XP visual
styles when available.
