Install headers in $prefix/include/$libname

Install each library's headers in $prefix/include/$libname.
The installed headers use #include "lib*/*.h"; applications
are expected to do the same.

Specify only $prefix/include in .pc files.

Originally committed as revision 12194 to svn://svn.ffmpeg.org/ffmpeg/trunk

libpostproc/Makefile

@@ -1,9 +1,6 @@
 
 include ../config.mak
 
-# Overload incdir, postproc include files go in a different directory.
-INCDIR=$(prefix)/include/postproc
-
 EXTRALIBS := -L$(BUILD_ROOT)/libavutil -lavutil$(BUILDSUF) $(EXTRALIBS)
 
 NAME=postproc
@@ -15,6 +12,3 @@ HEADERS = postprocess.h
 OBJS = postprocess.o
 
 include ../common.mak
-
-uninstall-headers::
-	-rmdir "$(prefix)/include/postproc"

libpostproc/postprocess.h

@@ -27,7 +27,7 @@
  *     external api for the pp stuff
  */
 
-#include "avutil.h"
+#include "libavutil/avutil.h"
 
 #define LIBPOSTPROC_VERSION_TRIPLET 51,1,0