build: Make folks optional

The dependency chain spirals out from folks->zeitgeist->xapian...and
I'm really not interested in pulling in all of that into the core
shell.

There is work on splitting out contact search into gnome-contacts; I'd
add a bug link but Bugzilla is down.

js/misc/config.js.in

@@ -6,6 +6,8 @@ const PACKAGE_NAME = '@PACKAGE_NAME@';
 const PACKAGE_VERSION = '@PACKAGE_VERSION@';
 /* 1 if gnome-bluetooth is available, 0 otherwise */
 const HAVE_BLUETOOTH = @HAVE_BLUETOOTH@;
+/* 1 if folks is available, 0 otherwise */
+const HAVE_FOLKS = @HAVE_FOLKS@;
 /* gettext package */
 const GETTEXT_PACKAGE = '@GETTEXT_PACKAGE@';
 /* locale dir */