Image2D pnpoly update

I sent the diff of this as an e-mail attachment to Chris, but I wanted to unburden him with this since it's not a critical change. Plus, it gives me an opportunity to do my first pull request! :-)

I added some PP functions and Perl wrappers to provide Image2d::polyfill-like routines to use the pnpoly algorithm for determining set membership. See sf.net bug 3535203 for details.

Many thanks.

- Tim