Add the signal race changes to x86-64 to make it compile again.

  Didn't merge the more pointless changes from i386.

  Also remove the special SA_ONESHOT handling, doesn't seem to be needed
  anymore.

From: Mikael Pettersson <mikpe@csd.uu.se>

  The signal-race-fixes patch in 2.6.8-rc2-mm1 appears to have broken
  x86-64's ia32 emulation.

  When forcing a SIGSEGV the old code updated "*ka", where ka was a pointer
  to current's k_sigaction for SIGSEGV.  Now "ka_copy" points to a copy of
  that structure, so assigning "*ka_copy" doesn't do what we want.  Instead do
  the assignment via current->...  just like the normal signal delivery code
  does.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>