More parallelization in MS File handlers

[jcnelson]

See if we can get the MS client to pass enough information to the handler such that on the fast path, we can load the Volume, Gateway, and MSEntry data we need in parallel, and perform the validations as we get the data back.

[jcnelson]

Moreover, it might be faster if we resolve a whole path at a time, instead of one directory at a time (but in parallel). Investigate both, and choose the faster one.