#70 clean up signal handling

[Stas Sergeev]

Currently there is a horrible mess of a silly
helper functions, like setsig, newsetsig, newsetqsig,
registersig, etc etc. And all this is working on top
of some magic dosemu_sigaction_wrapper().
I would suggest removing the unholly mess. It is
not obvious what flags are used and where. For instance,
I think we need SA_ONSTACK on all handlers, SA_RESETHAND
on most, SA_NODEFER on few and SA_SIGINFO/SA_RESTART
selectively, so it is silly to try hiding so many
combinations into a wrappers. I am sure the flags are
currently all wrong, but its too difficult to review.
I also suspect that much fewer signals need to be
handled.