Merge branch 'mm/config-xdg'

Teach git to read various information from $XDG_CONFIG_HOME/git/ to allow the user to avoid cluttering $HOME. * mm/config-xdg: config: write to $XDG_CONFIG_HOME/git/config file when appropriate Let core.attributesfile default to $XDG_CONFIG_HOME/git/attributes Let core.excludesfile default to $XDG_CONFIG_HOME/git/ignore config: read (but not write) from $XDG_CONFIG_HOME/git/config file