Escape calls for sed and awk in case someone aliased them (#264)

Co-authored-by: Jonathan Dahan <hi@jonathan.is>
Co-authored-by: rupa <rupa@lrrr.us>

Merge branch 'master' of github.com:rupa/z

version 1.8 PROMPT_COMMAND, cleanup

version 1.7 x and c options, prompt cmd append, revert exec warning

version 1.6 subdirs, option combining

version 1. exclude dirs

version 1.4 zsh changes (breaks backward compatibility)

version 1.3 tab completion improvements