autogen.sh: Support GNOME Build API

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

autogen.sh

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