accesslib: create_context() now populates the path of new contexts

accesslib: create_context() now populates the path of new contexts

... and it populates the context cache too.

Unfortunately, it needs an INSERT followed by an UPDATE. Other than
a stored procedure, I don't know how to deal with this better.

(We could save the SELECT though! that's a thought...)

OTOH, we are getting so much mileage out of the path field
that it's probably a hit we have to take in the chin and move on.