Remove our local patches for ucontext/pthread/fork model choice, since
this is handled by a configure argument now.
Note that ucontext is not supported on FreeBSD versions less than 5.0.
PR: 83245 (mostly)
Submitted by: Vasil Dimov <vd@datamax.bg>
Michael Trojnara[1].
Also, add the build-time WITH_FORK, WITH_PTHREAD, and WITH_UCONTEXT knobs
to control the stunnel threading model used, based on Vasil Dimov's PR's
with some modifications [2].
While I'm here, add in a <sys/types.h> inclusion that seems to be needed
for <ucontext.h> at least on FreeBSD 6.0/sparc64.
Reported by: many
Pointy hat to: roam (myself) for both not noticing this and then letting
it linger for a while
Obtained from: Michael Trojnara's BSD patch from
<53594c631989fde6ca0bdb3435b93dfe@mirt.net> [1]
PR: 81289, 82202 [2]
Submitted by: Vasil Dimov
