Automatically create working copy on import

[olsen232]

• sno init won't create a working copy, but it will store a default working copy location and working copy version in the repo config.
• sno init --workingcopy-path=some_path --workingcopy-version=some_version will override the defaults
• sno init --bare will create a repo which never has a working copy

The following commands all update the working copy. If no working copy is present (as happens on the first import), one will be automatically created using the info in the repo config:

• sno import
• sno checkout, sno switch, sno reset

[craigds]

is this done? I see de663b3 is in master.

Probably upgrade should also create a working copy, if there was one before the upgrade. At present it doesn't.