Various bug fixes

Various bug fixes

* In ?kickbanall, mod_chanmode_alloc(1) when we only use one arg.

* In ?modcmd ... channel_access, accept "0" to mean the same as "none."

* In log.c, make a single function to free the oldest log entry for a
log_type struct.

* Add more checks for cmd==NULL in chanserv.c:eject_user().
git-archimport-id: srvx@srvx.net--2004-srvx/srvx--devo--1.3--patch-22