Log Message:
Update py-argcomplete to 0.8.4.

Version 0.8.4 (2014-12-11)
- Fix issue related to using argcomplete in a REPL environement. Thanks
  to @wapiflapi (pull request #91).

Version 0.8.3 (2014-11-09)
- Fix multiple issues related to using argcomplete in a REPL environement.
  Thanks to @wapiflapi (pull request #90).

Version 0.8.2 (2014-11-03)
- Don't strip colon prefix in completion results if COMP_WORDBREAKS does
  not contain a colon. Thanks to @berezv (pull request #88).