Update some stuff related to the syscalls change:

Update some stuff related to the syscalls change:
 - restart syscalls which return ERESETARTSYS
 - make code to restart a syscall common
 - keep a process-wide pending signal set to store as-yet
   undelivered signals (only used in 2.4 mode; TODO: siginfo, queues)
 - make execve work a bit better - it is impossible to recover from
   execve failing, so we try to check that it will before running the
   syscall itself (also fixes bug with SuSE 8.2 kernel)

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@1964