MUC: Include old affiliation data in affiliation change event

MUC: Add room:set_affiliation_data()

MUC: Set .previous_affiliation = "none" if nil, for consistency with .affiliation It appears nothing currently uses this field in prosody or prosody-modules

MUC: Fix incorrect variable name (thanks luacheck)

MUC: Switch to event.allowed signaling to block event, matching muc-pre-set-role ...and fixing the logic bug that broke everything in the previous commit.

MUC: Add 'muc-pre-set-affiliation' event, allowing to block change or modify data

MUC: Add option to include form in registration query This was originally not done based on my interpretation of XEP-0045. Today's reading, however, revealed that it actually says the result > SHOULD contain **at least** a <username/> element (emphasis mine) I take this to mean that including a form **is** allowed (and I think this is sensible). Tigase already includes the form I believe. I've gated the new behaviour behind a (default off) option, because it hasn't been tested for compatibility with clients. My primary desire for it is in Snikket, where the clients will be tested to ensure compatibility with this. I don't anticipate that (m)any clients would break, so maybe after 0.12 we can experiment with enabling it by default and eventually remove the option.

mod_admin_shell: Handle absence of connection in security column (thanks arcseconds) I surmise this can happen in a disconnected/smacks hibernation state.

mod_pubsub: Fix traceback in disco of non-existent node (thanks Martin) In this case `ret` is a table not containing the node, which makes pubsub_error_reply() try to get an error template with that `ret` table as index, which returns a `nil` then passed to table.unpack, which in turn throws the error.

net.connect: Prefer last connection error over last resolver error E.g. "connection refused" over one IP version instead of NoError for the other IP version.