This new approach allows filtering out checks from the default set that are
not appropriate for a command, rather than having to list every check
that is appropriate. It also reduces some boilerplate.
Haskell does not define Eq for functions, so I had to go a long way around
with each check having a unique id. Meh.
* git-annex now asks git-annex-shell to verify that it's operating in
the expected repository.
* Note that this git-annex will not interoperate with remotes using
older versions of git-annex-shell.
The reason for this check is to avoid git-annex getting confused about
what remote repository actually contains a value. It's a prerequisite for
supporting git insteadOf aliases.
* Look for dir.git directories the same as git does.
* Support remote urls specified as relative paths.
* Support non-ssh remote paths that contain tilde expansions.
