Add a preexec hook to set the GPG-Agent TTY

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
Check for S.gpg-agent to see if gpg-agent is running

From GnuPG changelog:

>  Removed the GPG_AGENT_INFO related code.  GnuPG does now
>  always use a fixed socket name in its home directory.

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
Fix issue with several themes where errors occur
if the git module is not loaded.
Fix Powerline unicode characters

Branch & separator characters are updated to display properly.
[Fix #748] Set grep color for BSD and GNU
Revert "Remove extra git-dir call in git-info and use git_dir variable instead"

This reverts commit 3012c0984b2b3fd97a58ac9dad1ae54efc546e49.
Merge branch 'master' of https://github.com/sorin-ionescu/prezto