Escape regexp used to match nick in CTCP replies

Originally created by @anonym on #10219 (Redmine)

Look at this from the CTCP helper:

    if m.ctcp? and /^:#{@spam_target}!/.match(m)

Our Pidgin nick’s have a 10% chance to include a ^, which will break that regexp. We need to escape all characters in the nickname.

Feature Branch: test/10219-escape-nick-for-ctcp-responses

Parent Task: #8539 (closed)