Support the SSH-2 mechanism for sending signals to a running session. Neither

Support the SSH-2 mechanism for sending signals to a running session. Neither
of the SSH servers I conveniently have access to (Debian stable OpenSSH --
3.4p1 -- and lshd) seem to take a blind bit of notice, but the channel
requests look fine to me in the packet log.

I've included all the signals explicitly defined by
draft-ietf-secsh-connect-19, but I've put the more obscure ones in a submenu
of the specials menu; there's therefore been some minor upheaval to support
such submenus.

git-svn-id: svn://svn.tartarus.org/sgt/putty@4652 cda61777-01e9-0310-a592-d414129be87e