Give "robbyrussell" them support for the timed-out check.
Uses zsh's `coproc` to put a timeout on the `git status` call inside git_prompt_info()
Introduces $ZSH_THEME_GIT_PROMPT_TIMEDOUT and $ZSH_THEME_SCM_CHECK_TIMEOUT theme configuration variables to control how long the timeout is and how the timed-out indicator appears inside the prompt.