The terminal window can now indicate that PuTTY is busy in various ways, by

The terminal window can now indicate that PuTTY is busy in various ways, by
changing its mouse pointer. Currently this is only used in the (slightly-
arbitrarily-defined) "heavy" bits of SSH-2 key exchange. We override pointer
hiding while PuTTY is busy, but preserve pointer-hiding state.

Not yet implemented on the Mac.

Also switch to frobbing window-class cursor in Windows rather than relying on
SetCursor().

git-svn-id: svn://svn.tartarus.org/sgt/putty@5303 cda61777-01e9-0310-a592-d414129be87e