Move circulation, copy and user checks to check_circ_details method.

Move circulation, copy and user checks to check_circ_details method.

Before implementing renewitem in NCIP::ILS::Evergreen, it became
apparent that we'd want to make the same checks for the copy being
checked out, owned by or checked out at our working ou, and being
checked out to the provided user, if any, before proceeding with
renewal. It makes sense therefore to move the checks from being
inside checkinitem to being its own function that returns a
NCIP::Problem or undef.

Signed-off-by: Jason Stephenson <jason@sigio.com>