Remove untested mounting/unmounting volumes within volumes code.
Now that we have the automount daemon, we'll have the slivers
mount/unmount volumes within volumes if this is desired.
Added directory pagination for reading directories with more than
ms.common.RESOLVE_MAX_PAGE_SIZE items.  The MSEntry.ListDir() method
allows callers to specify a page ID and a start cursor, and will cache
the page-worth of listings for subsequent listing (and rely on the
directory's write-nonce to distinguish between fresh and stale
listings).  Libsyndicate has been updated to list directories one page
at a time, using the page size given to the gateway on registration.

Still to come: ensuring that the client can't forge a cursor, and cause
memcache poisioning on the MS.