Merge pull request #70 from l/translation_ja

core: update Japanese translations
core: add check of .po files with msgcheck for Travis
core: add install of package libenchant-dev for Travis

Package libenchant-dev is required by pyenchant (used in msgcheck).
core: remove use of virtualenv for Travis
core: add option "APT::Install-Recommends=false" for apt-get (Travis)
core: set option APT::Install-Recommends before commands apt-get / mk-build-deps (Travis)
core: use tee to write in /etc/apt/apt.conf (Travis)
core: use before_script instead of before_install (Travis)
core: add missing semicolon in .travis.yml
irc: add option irc.look.join_auto_add_chantype (closes #65)
xfer: fix problem with option xfer.file.auto_accept_nicks when the server name contains dots
core: update German translation
Merge branch 'master' of https://github.com/weechat/weechat
doc: update German auto-generated files
relay: add support of Internet Explorer websocket (closes #73)
core: add support for negated tags in filters (closes #72)
core: add parentheses around tests in conditions
core: add support of '!' for tags in /help filter
core: update ChangeLog (add support of negated tags in filters)
relay: fix disconnection of client on empty websocket frames

WeeChat disconnects any client when a frame with length 0 is recieved.