Only digest entities if not present in the charm store.
Better name for bzrDigestKey.
Exclude existing entities in a separate function.
Better code organization and improve digest logging.
Avoid setting the request content length where not required.
Improve doCharmStoreRequest documentation.
Implement charmStoreGet and charmStorePut helper functions.
Merge pull request #111 from frankban/revision-info

Only digest entities if not present in the charm store.

Store the bzr-digest extra-info for all the ingested entities, and compare the value in subsequent charmload calls.
Merge branch 'v4' of github.com:juju/charmstore into ingest-bundles

Conflicts:
	lppublish/lpad.go