-----------------------------
By introducing a new sigframe so that the signal handler operates
on the new siginfo_t and on ucontext_t instead of sigcontext, we
now need two version of sendsig and sigreturn.
A flag in struct proc determines whether the process expects an
old sigframe or a new sigframe. The signal trampoline handles
which sigreturn to call. It does this by testing for a magic
cookie in the frame.
The alpha uses osigreturn to implement longjmp. This means that
osigreturn is not only used for compatibility with existing
binaries. To handle the new sigset_t, setjmp saves it in
sc_reserved (see NOTE).
the struct sigframe has been moved from frame.h to sigframe.h
to handle the complex header dependencies that was caused by
the new sigframe.
NOTE: For the i386, the size of jmp_buf has been increased to hold
the new sigset_t. On the alpha this has been prevented by
using sc_reserved in sigcontext.
Move sigjmp_buf and jmp_buf structure definitions to machine/setjmp.h
so that i386 can continue to use int as the basic register type and
alpha can use long. Bruce was concerned about possible differing
alignment. I've left the definition of _JBLEN in machine/setjmp.h
even though Bruce's example used the number directly. I don't know if
any other code relies on _JBLEN, so I left it to avoid potential
breakage.
