stgit restrictions on patch names

Looks like stgit is now more picky on patch names than in used to be:

$ stg branch --clone v2.0.6-debian
Checking for changes in the working directory ... done
Cloning current branch to "v2.0.6-debian" ...
  No log for 01_springelectrical
stg branch: Invalid patch name: "10_g++4.0_build_failures"
$

=> the result of the cloning operation is a partial clone.  Do we want to:

- implement a mechanism for checking beforehand that the operation
will not fail ?  Seems awkward to duplicate checks already found
elsewhere.

- wait for proper transactions so we can rollback on error ?

- on clone error, delete the newly-created stack ?  I'd vote for this
one, until the previous one gets done.

=> is there any particular reason why we would refuse "+" ?