Add missing exec_prefix entry in pipi.pc.in.

git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@3645 92316355-f0b4-4df1-b90c-862c8a59935f

pipi/pipi.pc.in

@@ -1,4 +1,5 @@
 prefix=@prefix@
+exec_prefix=@exec_prefix@
 libdir=@libdir@
 includedir=@includedir@