mod_component: Handle component connecting to non-existent host

mod_motd: Use presence/bare to catch a client's initial presence and send the MOTD then (fixes #282)

multiplex_listener: Remove (already ported to mod_net_multiplex)

modulemanager: For children of shared modules, set module.environment to the empty environment for that module (useful to expose data or APIs at host.modules[module])

moduleapi: Have modules internally store a reference to shared tables they use, to ensure they don't get collected while any module that had access to that table is still loaded (thanks Zash)

mod_component: Make a shared module, and move the xmppcomponent_listener into it ('port'ing over to portmanager). Ha ha.

mod_motd: Send only to resource coming online, not the user's bare JID (fixes #282)

prosody: Don't require net.httpserver now

mod_admin_telnet: module:load(): Fix 'global-module-already-loaded' errors when successfully loading a global module (fixes #228)

mod_admin_telnet: module:list(): List global modules (part-fixes #228)