util.format: Fix Lua 5.1 quirks thanks to ALL THE TESTS

util.format: ALL THE TESTS!!! The more tests I made, the more Lua 5.1 quirks I discovered. Tests generated using a tool plus some touch-up.

util.format: Also handle the %p format added in Lua 5.4

util.format: Ensure sanitation of strings passed to wrong format Ie. log("debug", "%d", "\1\2\3") should not result in garbage. Also optimizing for the common case of ASCII string passed to %s and early returns everywhere. Returning nil from a gsub callback keeps the original substring.

util.format: Escape invalid UTF-8 by passing trough serialization Should prevent invalid UTF-8 from making it into the logs, which can cause trouble with terminals or log viewers or other tools, such as when grep determines that log files are binary.

mod_mam: Avoid storing bounces for messages from the bare account (thanks Ge0rG) This should rule out error replies to PEP notifications, which come from the account bare JID, and would be reflected back to it if they can't be delivered for some reason, e.g. s2s problems.

MUC: Remove <{muc}x> tags in some errors Including the payload of the stanza that caused the error is optional and we're generally not doing it anywhere else.

MUC: Fix error origin JID in wrong argument position Mistake introduced in cbe524ed1a6a. Removing because this is a query to the bare JID where the error origin matches the resulting stanza 'from'.

MUC: Remove remaining deprecated numeric error codes The numeric error codes seems to have been removed from the examples in XEP-0045 version 1.24, and were deprecated even by RFC 3920 in 2004, only allowed for backwards compatibility.

MUC: Return a friendly textual error when trying to speak without voice I spend several minutes confused over where the bug was until I remembered I had set myself as visitor in the previous debug session. This would have helped.