fix out of tree builds

This allows you to build out of tree like:
	mkdir build
	../configure
	make

This also fixes `make distcheck` since that uses the above mechanism.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Jeff Mahoney <jeffm@suse.com>

configure.ac

@@ -118,6 +118,8 @@ if test "x$ac_cv_wuninitialized_flag" = xyes; then
 	CFLAGS="$CFLAGS -Wuninitialized"
 fi
 
+CPPFLAGS="-I\$(top_srcdir)/include $CPPFLAGS"
+
 AC_OUTPUT(
     include/Makefile 
     mkreiserfs/Makefile