[pitivi] Fix make distcheck

[Thibault Saunier <tsaunier src gnome org>]

commit 438930e98ff2a9714ccd3eae1a90fded0874f56a
Author: Wim Taymans <wtaymans redhat com>
Date:   Fri May 22 16:10:19 2015 +0200

    Fix make distcheck

 pitivi/libpitivi/Makefile.am |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/pitivi/libpitivi/Makefile.am b/pitivi/libpitivi/Makefile.am
index 39080cf..2d5f821 100644
--- a/pitivi/libpitivi/Makefile.am
+++ b/pitivi/libpitivi/Makefile.am
@@ -22,8 +22,9 @@ lib_LTLIBRARIES = libpitivi-1.0.la
 
 INTROSPECTION_GIRS = Pitivi-1.0.gir
 
-introspection_source_h = $(source_h)
-introspection_source_c = $(source_c)
+introspection_source_h = $(patsubst %,$(srcdir)/%, $(source_h))
+introspection_source_c = $(patsubst %,$(srcdir)/%, $(source_c))
+
 Pitivi-1.0.gir: $(INTROSPECTION_SCANNER) libpitivi-1.0.la
                $(INTROSPECTION_SCANNER) -v --namespace Pitivi \
                --nsversion=1.0 \