Added completion for Homesick
(https://github.com/technicalpickles/homesick). Originally from
https://github.com/liborw/homesick-completion.
fix bug where "no active gemsets" displayed to STDERR
Merge pull request #259 from marshally/fix_rbenv_gemset_bug

fix bug where "no active gemsets" displayed to STDERR
Merge pull request #258 from nwinkler/homesick-completion

Added completion for Homesick
Merge remote-tracking branch 'upstream/master'