Only install libswscale.pc and swscale headers when needed.

This is in the process to be submitted upstream

extras/contrib/src/Makefile

@@ -908,6 +908,7 @@ DISTCLEAN_PKG += libmatroska-$(LIBMATROSKA_VERSION).tar.bz2
 ffmpeg:
 	$(SVN) export $(FFMPEG_SVN)  ffmpeg
 	(cd "$@" && patch -p1 < ../Patches/ffmpeg-svn-nofile.patch)
+	(cd "$@" && patch -p0 < ../Patches/ffmpeg-svn-swscale-pc.patch)
 ifeq ($(HOST),i586-pc-beos)
 	(cd $@; patch -p0 < ../Patches/ffmpeg-svn-beos.patch)
 endif

extras/contrib/src/Patches/ffmpeg-svn-swscale-pc.patch

+Index: Makefile
+===================================================================
+--- Makefile    (revision 8597)
++++ Makefile    (working copy)
+@@ -149,7 +149,9 @@
+ ifeq ($(CONFIG_PP),yes)
+ 	(MAKE) -C libpostproc install-headers
+ endif
++ifeq ($(CONFIG_SWSCALER),yes)
+ 	$(MAKE) -C libswscale  install-headers
++endif
+
+ uninstall: uninstall-progs uninstall-libs uninstall-headers uninstall-man uninstall-vhook
+