Log Message:
Fix i386 signal handler.

ocaml has a twisty maze of ifdefs to define signal handler types and
obtain the faulting address.  NetBSD no longer has sigcontext
(available to user space) and instead the more POSIXy ucontext; this
commit changes the patch to use that.

Fixes build on i386, and the resulting package can run unison.  In
theory !i386 is unchanged.