Fix various breakages my Carbonisation caused in the Classic build, notably

that outside Carbon, CGrafPtr and GrafPtr are different types, even though
they're mostly interchangeable, so we need to interpose a cast between
GetWindowPort and SetPort.

git-svn-id: svn://svn.tartarus.org/sgt/putty@2790 cda61777-01e9-0310-a592-d414129be87e