[Fix #355] Do not set launchd environment variables

Setting environment variables for launchd processes is unreliable.
Finder and all Finder launched programs have to be restarted for the
new environment variables to take effect.
[Fix #357] Set alias gcO to check out hunks interactively
Changes to emacs alias
Do not share history between all sessions
Merge branch 'master' of https://github.com/sorin-ionescu/prezto
external changes