Additional plugins for GMPC.

avahi, awn, lirc, microhttpd, and webkitgtk are optional deps.
Some of these are available at SlackBuilds.org. If you have any
of these and would like to enable the plugin, the variables are
as follows: AVAHI AWN LIRC MSERVER WIKIPEDIA

For example, if you have avahi and lirc, you would do this:
	AVAHI=yes LIRC=yes ./gmpc-plugins.SlackBuild