admin-command: add verify command Start using the 'admin' namespace by adding a 'verify' command. Invocation is 'admin::verify'. The idea is to progressively add more focused checks than the existing verify command. To do so we need an advanced way to express what we want to check. The first check for admin::verify is 'working-copy.dirstate' which has no options, because it was an easy first check to implement, which verifies the integrity of the dirstate. This changeset was created with the help of Franck Bret.

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.