compare s3's last modified time using server's timezone

S3's last modified time is stored in utc timezone,
but displayed in server's timezone.
Prior to this fix, no timezone calculation was made,
so test_ls_command.py kept failing for some timezones.

This fix tests displayed last modified time using server's timezone.
Add ability to immediately shutdown executor

Switch the task queue to a priority queue and allow
ShutdownThreadRequest (which originally were just the QUEUE_END_SENTINEL
object) to have a more important priority in the case that a user
has hit Ctrl+C.
Add stable priority queue for task queue

This is needed to provided FIFO semantics to the task queue
for objects of the same priority.

We only need to be able to preempt workers with high priority
items.  Otherwise everything should be in FIFO order.
Remove dateutil as a dep, not needed

botocore pulls in a dep on dateutil.
Merge branch 'quiver-fix-s3-lastmodified-tz-oddity' into develop

* quiver-fix-s3-lastmodified-tz-oddity:
  Remove dateutil as a dep, not needed
  compare s3's last modified time using server's timezone
Merge branch 'immediate-s3-exit' into develop

* immediate-s3-exit:
  Add stable priority queue for task queue
  Add ability to immediately shutdown executor
Don't remove paging params from arg table, hide them

This allows us to add pagination configs after the fact and
still remain backwards compatible with users performing their own
pagination.

The new logic is to support the manual, per-service pagination
arguments, but not document them.  If we see that the user has provided
manual pagination arguments, we automatically switch `--no-paginate`
on.

This keeps pagination backwards compatible.  If a user was manually
paginating responses:

    aws service op --next-marker foo

And we add pagination configs to the service, then the previous command
will still work because we'll detect the --next-marker argument
corresponds to a pagination arg, we'll instruct the CLI to not auto
paginate, and the user will have the same behavior.
Merge branch 'hide-page-params' into develop

* hide-page-params:
  Don't remove paging params from arg table, hide them
Don't run Ctrl+C test on windows

SIGINT not supported.