[dev] [dmenu] Patch for XDG Base Directory specification of dmenu_path

Hi all,

Attached is a patch to dmenu_path which (if enabled in the config.mk)
changes the cache file location to be XDG Base Directory Specification
compliant. After enabling the change, the cache file will live at
$XDG_CACHE_HOME/dmenu/path.cache (or $HOME/.cache/dmenu/path.cache if
$XDG_CACHE_HOME is not set), rather than in the home directory at
~/.dmenu_cache.

This patch relies on libxdg-basedir [2] being installed.

Thanks for dmenu!

-- 
- Jon Raphaelson
[1] http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
[2] http://repo.or.cz/w/libxdg-basedir.git