Summary:
Include tools/lfs in the shipit path map for now, since it is needed to
download vendored Rust crates on internal builds.  Also correctly indicate
that the fb-mercurial* dependencies also apply only to internal builds.

Reviewed By: chadaustin

Differential Revision: D18621421

fbshipit-source-id: 74f00bf318ff9aefdca8696a61a8f33587749e66