Log Message:
* fixes build with xulrunner-2, include mozilla-config.h unconditionally.
  PR#45110.
* change dependency on xulrunner to build only.

Not bump PKGREVISION, because it is inpossible to build after dependency was
switched to xulrunner-2.
XXX: still firefox-4.1 does not recognize this plugin as add-on for me.