added option to ignore empty or small objects

adding `min_size:1` or any other integer to `device` definition in job description
will instruct objectquery middleware to ignore objects of the size smaller than `min_size`
it can be good for various error channels, for example placing `min_size:1` on `stderr` and saving `stderr` as object
will produce the object only in case where `stderr` was not empty
Merge pull request #94 from pkit/empty_objects

added option to ignore empty or small objects
requirements.txt: pin swift 1.13.1

With the release of swift 2.0.0, some tests in ZeroCloud broke.

This commit
https://github.com/openstack/swift/commit/3824ff3df71975194fa1b050255c0da8c1acc598
took away the `object_ring` kwarg from the
swift.proxy.server.Application class, which the ZeroCloud tests were
using.

Until we can update everything to be compatible with swift 2.0, we can
stay at version 1.13.1.
Merge pull request #96 from larsbutler/pin-swift-to-1.13.1

requirements.txt: pin swift 1.13.1