deb: added Release file to each individual arch dir for d-i.
Added tests for Release file in distribution directory
Handle source repos while creating dist release file
Merge branch 'debinst' of https://github.com/ryanuber/aptly into ryanuber-debinst

Conflicts:
	deb/publish_test.go
Refactoring, support for atomic updates and checksumming. #61
Update tests with introduction of Release files under each arch/component. #61