autogen.sh: Honor NOCONFIGURE=1

(Also while we have the patient open, use exec instead of hanging
 around uselessly in waitpid)

http://people.gnome.org/~walters/docs/build-api.txt

Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Colin Walters <walters@verbum.org>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

autogen.sh

@@ -9,4 +9,6 @@ cd $srcdir
 autoreconf --force -v --install || exit 1
 cd $ORIGDIR || exit $?
 
-$srcdir/configure "$@"
+if test -z "$NOCONFIGURE"; then
+    exec $srcdir/configure "$@"
+fi