Add mkv file extension as ffmpeg now can mux to Matroska.

Preferences for dummies ( #603 ) is now almost done in Qt4. Please test and review my commits.

Qt4 - Preferences, don't remove the widgets to re-add them! Just use hide/show... A stackedLayout would have been a better idea, but this should work.
Please report any breakage, as it might be wrong somewhere.

Qt4 - Prefs; cleaning, disabling unused code, general comments, class renaming, in order to actually use those preferences. :D

Gosh, who wrote those simple Preferences ? Seriously ?
ooooooooooooooops...

The change in configure.ac is suboptimal. It would be better to change DEFAULT_INCLUDES to use -I${top_builddir}/include rather than -I${top_builddir}. Automake wizard requested.

net/if.h depends on it on some systems (Darwin & FreeBSD at least)

Qt4 - SPrefs, device selection. Please Review, since I am far from sure that this is a good idea... 
Moreover, is it config_PutPsz( p, name, ASCII ) or  config_PutPsz( p, name, UTF-8 )  ?

* fixed Apple Remote support for Leopard. Note that the cookie for kRemoteControl_Switched wasn't updated, but since we don't use this feature in VLC, that's pretty fine.