Remove the FreeBSD 3.x signal code. This includes osendsig(),

Remove the FreeBSD 3.x signal code.  This includes osendsig(),
osigreturn() and a couple of structures that these syscalls depended
on.

Split the sigaction(), sigprocmask(), sigpending(), sigsuspend(),
sigaltstack() and kill() syscalls.

Move the 4.3BSD signal syscalls osigvec(), osigblock(), osigsetmask(),
osigstack() and okillpg() to the 43bsd subtree.  I'm not too sure
if these will even work with the FreeBSD-4 signal trampoline code,
but they do compile and link.

Implement linux_signal(), linux_rt_sigaction(), linux_sigprocmask(),
linux_rt_sigprocmask(), linux_sigpending(), linux_kill(),
linux_sigaction(), linux_sigsuspend(), linux_rt_sigsuspend(),
linux_pause(), and linux_sigaltstack() with the new in-kernel syscalls.
This patch kills 7 stackgap allocations in the Linuxolator.