Vcs.Mock_revsMaintaining a mapping between mock revs and actual revs.
This is used to build reproducible tests.
t is a mutable data structure that holds a bidirectional mapping between actual and mock revisions.
val create : unit -> tAdd a binding between a revision and a mock revision. This raises if such revisions are already bound in t.
Given a revision of an actual repository, resolve it and return the mock revision that is bound to it in t. If this rev isn't bound to any mock rev in t yet, this function will call next to build a new mock revision, bind it in t and return it.