Refactor how projects parse remotes so it can be replaced

We now feed Project a RemoteSpec, instead of the Remote directly
from the XmlManifest.  This way the RemoteSpec already has the
full project URL, rather than just the base, permitting other
types of manifests to produce the URL in their own style.

Signed-off-by: Shawn O. Pearce <sop@google.com>
4 files changed