xfer: Use hook_connect() for receiving chats

fixes #160
xfer: bind to wildcard address when sending

When #5 was fixed, we started to always bind to the local address
connected to the irc server because the xfer.network.own_ip address
may not be able to be bound to when NATed. But this means when the
own_ip address is a different family (IPv4 vs IPv6) from the irc
server connection, we were listening for connections on the wrong
interface.

This patch lets us figure out which family is being used,
(xfer.network.own_ip's family, or the irc connection's family
otherwise) and bind() into the correct family via that family's
wildcard address.
tests: add tests of functions string_shared_get and string_shared_free
relay: disable SSLv3 by default

The new default value for option relay.network.ssl_priorities is now
"NORMAL:-VERS-SSL3.0".
irc: disable SSLv3 by default in server option "ssl_priorities" (closes #248)
irc: use option irc.look.nick_mode_empty to display nick prefix in bar item "input_prompt"
doc: add "beep" trigger in question about highlights (FAQ)
core: add bar item "mouse_status", new options weechat.look.item_mouse_status and weechat.color.status_mouse
core: update translations
core: update ChangeLog
core: update German translations
python: remove comment added by mistake
doc: update German auto-generated files
doc: add list of bar items not used in bars by default (user's guide)
core: add Travis CI builds with Python 3 and without GnuTLS
doc: update German documentation
core: add option weechat.completion.command_inline (task #12491)
core: update German translations
doc: update German auto-generated files
Merge branch 'xfer_wildcard' of git://github.com/talisein/weechat-1 into talisein-xfer_wildcard