Naive mirroring implementation
keys and secrets
Added config entry for source_index
Reworked source_lookup, storing json/ancestry/etc locally, removed decorator (obsolete)
Tags are mutable, they shouldn't be stored on mirrors
Added tags caching support (with TTL)
pep8 fix
Tags cache ttl expressed in seconds, small bugfixes, minor improvements
Reimplemented cleaned up mirror decorator
Applied source_lookup decorator on relevant methods
Added tags lookup decorator (and caching logic). Cleanup.
bugfixes
miscellaneous fixes
Mirror unit tests
Moved mirroring decorators and utils to lib/mirroring.py
Using mirroring decorator on index route (for standalone mirrors)
Merge branch 'master' of https://github.com/dotcloud/docker-registry into mirroring

Conflicts:
	registry/index.py
	registry/tags.py
lib/mirroring: Rewrote confusing code

Docker-DCO-1.1-Signed-off-by: Sam Alba <sam.alba@gmail.com> (github: samalba)
tags: typo, is_mirror() function moved

Docker-DCO-1.1-Signed-off-by: Sam Alba <sam.alba@gmail.com> (github: samalba)
Some refactoring, especially config is more intuitive

Docker-DCO-1.1-Signed-off-by: Sam Alba <sam.alba@gmail.com> (github: samalba)