Previously we used a global variable to track if the incoming connection was
from a shallow remote (based on if the network command was a *_shallow command).
This is hacky and overall a bad idea. The new implementation stores the shallow
flag as a bundlecapability passed to the getbundle command.
A side effect of this is remotefilelog won't work with versions of mercurial
that don't use the getbundle command.
The remotefilelog extension currently doesn't work with tags. Adding include and
exclude patterns allows users to specify which files they want to treat as
shallow and which the want to download the entire history for. By excluding
.hgtags from being shallow, this enables tags to work in a mostly shallow repo.
This also enables largefile like scenarios where most files are full and only a
few large ones are kept remote.
When the cache is stored on a filesystem, excessive stat calls can slow
mercurial updates down dramatically. This reduces it to a single open call for
the cache location and if that fails, a single open call for the local location.
