bot.py: remove max_messages assignment inside say

max_messages value not passed through to bot.msg, breaking chunking up of messages larger than 400 chars
irc.py: decrement max_messages when recursing msg()

msg() doesn't honor max_messages without decrementing it when recursing
Merge pull request #298 from Preston4tw/patch-1

[core] Fix the limiting of the number of pieces a message can be split.