Merge pull request #105 from l/translation_ja

core: update Japanese translations
doc: update Japanese auto-generated files
core: update URL of WeeChat screenshot in README.asciidoc
irc: add value "+" for option irc.look.smart_filter_mode to use modes from server prefixes (closes #90)

The new default value of option irc.look.smart_filter_mode is now "+".
core: update German translations
doc: update German documentation
doc: update German auto-generated files
irc: fix typo in a message
core: update German translations
doc: update German auto-generated files
core: fix typo in German message
core: add option "env" in command /set
core: remove extra spaces in /help set
core: add missing declaration of "environ" (fix compilation on Mac OS X)
core: update German translations
doc: update German auto-generated files
core: fix completion of environment variable value when beginning of value is given
core: fix completion of plugins commands when beginning of command is given
core: do not display content of passphrase on /secure buffer
core: remove obsolete translations