Reject duplicate assignments of tasks
Bugfix for setting return codes in accept handler

The HTTP return code must be set before any actual output is written,
otherwise it has no effect.
Merge pull request #60 from guidow/error_code_bugfix

Bugfix for setting return codes in accept handler
Set comprehension is python 2.7+, don't use it
Merge pull request #59 from guidow/reject_duplicate_assignments

Reject duplicate assignments of tasks
adding --use-mirrors to hopefully cut down on failures
forgot, --use-mirrors was deprecated
retrying pip installs
source retry instead of executing it
Merge branch 'master' of github.com:pyfarm/pyfarm-agent into master_reannounce