changes to !uset autoinvite behavior, introduction of allchanmsg_func hooks

* changes to !uset autoinvite behavior: the autoinvite flag now works whether or not the channel it is set in is +i/+k.

* introduction of allchanmsg_func hooks: there is now a set of hooks (available via reg_allchanmsg_func()) in place to catch all public channel messages the services server sees.

git-archimport-id: srvx@srvx.net--2004-srvx/srvx--devo--1.3--patch-46