Request for swapcontext and getcontext to be ported to our libc

[users-errors at crater.dragonflybsd.org]

    I found one other issue, and that is we can't really determine
    whether the FP unit is being used from userland or generate an
    exception-on-first-use visible to userland, which means we can't
    optimize-out the FP state save/restore.  I don't think this 
    is a showstopper, though.  For now we can just unconditionally
    save/restore the FP state... it only takes 69ns or so on my
    test box for a save+restore sequence.  Later on the kernel can 
    easily supply the required information via shared memory or
    something similar (along with the signal mask and pending bits).

    Either way, just doing it uncoditionally is still far faster then
    making a system call.

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>