Make xvmc.h an installed header, applications like MPlayer need it.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@17226 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/Makefile

@@ -3,7 +3,7 @@ include $(SUBDIR)../config.mak
 NAME = avcodec
 FFLIBS = avutil
 
-HEADERS = avcodec.h opt.h vdpau.h
+HEADERS = avcodec.h opt.h vdpau.h xvmc.h
 
 OBJS = allcodecs.o                                                      \
        audioconvert.o                                                   \