Safely add reattach-to-user-namespace
Merge pull request #419 from maletor/patch-3

Safely add reattach-to-user-namespace
Fix path to zsh to use the homebrew installed newer version
Fall back to /bin/zsh if /usr/local/bin/zsh doesn't exist
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Fall back to /bin/zsh if /usr/local/bin/zsh doesn't exist
  Fix path to zsh to use the homebrew installed newer version
  Safely add reattach-to-user-namespace