Changelog cosmetics
removed centos/celeryd CELERYD_CHDIR quoting
Merge pull request #1989 from ffeast/centos-initd-chdir

removed centos/celeryd CELERYD_CHDIR quoting
Correct import in security docs.
Merge pull request #1992 from iandees/patch-1

Correct import in security docs
Update AbortableTask docs.  Closes #1993