add users file
add SyncPersonsOnSlice() and supporting functions
add slice users list support
pass addusers option to slice.sync
use user's user_list
Merge branch 'master', remote-tracking branch 'upstream/master' into add-users-to-slices
clarify comment
Merge pull request #17 from stephen-soltesz/add-users-to-slices

Add users to slices
Merge branch 'master', remote-tracking branch 'upstream/master'
all CentOS all the time