Fix distcheck.

Before this change gst/__init__.py wasn't being copied to
$(top_builddir)/gst/, making make check fail to import gst.

configure.ac

@@ -421,4 +421,5 @@ AC_OUTPUT([
   testsuite/Makefile
   win32/common/config.h
   gst-python.spec
+  gst/__init__.py
 ])

gst/Makefile.am

@@ -82,7 +82,7 @@ GST_OVERRIDES = 		\
 GST_DEFS = gst.defs gst-types.defs gst-extrafuncs.defs libs.defs base.defs
 CLEANFILES = gst.c
 EXTRA_DIST += $(GST_DEFS) $(GST_OVERRIDES) gstversion.override.in
-gst.c: $(GST_DEFS) $(GST_OVERRIDES) $(GEN_FILES) gstversion.override
+gst.c: $(GST_DEFS) $(GST_OVERRIDES) $(GEN_FILES) gstversion.override __init__.py
 
 # GStreamer interfaces bindings
 interfaces_la_CFLAGS = $(common_cflags) $(GST_PLUGINS_BASE_CFLAGS)