[Koha] API for circulation modules

[Tonnesen Steve]

I've added my API for circulation modules to the cvs repository
(C4/Circulation/Circ2.pm), as well as my latest tk circulation interface
(/tkperl/tkcirc) which depends on Circ2.pm.

Some things I know I'm still missing:

Branch and printer selection

I don't create a database handle in the circulation code itself.  This
means that the subroutines in Circ2.pm must open and close a database
handle with each call.  I don't know if this delay hurts overly much, but
it's there.  I've been thinking that I should create the the database
handle in the circulation code and pass it to the subroutines.  If the
database handle isn't defined, the subroutines can always create their
own as a fallback.

My understanding of the accounting system underlying Koha is scratchy at
best.  I just copied the accounting code from the existing interface...

Still missing payment option in the interface (and the API, for that
matter).  

Steve