preparation for exec.

* syscall:
	add syscall.RawSyscall, which doesn't use sys.entersyscall/sys.exitsyscall
	add syscall.dup2
	add syscall.BytePtrPtr
	add syscall.Rusage, RusagePtr
	add syscall.F_GETFD, F_SETFD, FD_CLOEXEC

* runtime:
	clean up, correct signal handling.
	can now survive (continue running after) a signal.

R=r
DELTA=394  (286 added, 51 deleted, 57 changed)
OCL=20351
CL=20369
19 files changed
tree: c5608a8146ee938d88da7942dd5bb4a17dc904ea
  1. doc/
  2. include/
  3. lib/
  4. pkg/
  5. src/
  6. test/
  7. usr/