transaction: abstract away the detection of an abandoned transaction We're about to add another place where this is used, let's not spill this implementation detail.

commands: add admin namespace In order to stop abusing the 'debug' namespace for non-debug command, it adds a new 'admin' namespace dedicated to 'admin' operations on a repository (i.e commands suitable for administration tasks). This namespace entry would be used to migrate in the future some existing commands from the 'debug' namespace, or other top level commands that may not be directly exposed to end users. (verify command is a perfect candidate for this case)

revlog: make the rust test for node hex prefix resolution exercise the nodemap

revlog: fix a bug where NULL_NODE failed to be resolved to NULL_REV The problem is that nodemap already takes care about NULL_NODE resolution (in `validate_candidate` in `nodemap.rs`), so the special handling in `rev_from_node` is unnecessary and incorrect.