install: add func to set a var in launchd.conf

Signed-off-by: Christopher Larson <kergoth@gmail.com>
mercurial: only install if hg is available

Signed-off-by: Christopher Larson <kergoth@gmail.com>
setup-osx: fix brew install of reattach-to-user-namespace

Signed-off-by: Christopher Larson <kergoth@gmail.com>
vim: create XDG_CACHE_HOME/vim if missing

Signed-off-by: Christopher Larson <kergoth@gmail.com>
vim: set VIMINIT in launchd.conf for macvim

Signed-off-by: Christopher Larson <kergoth@gmail.com>
setup-brew, setup-python: WIP scripts for further osx setup

Signed-off-by: Christopher Larson <kergoth@gmail.com>