Fix select failures when STDIN is ready.

Fix select failures when STDIN is ready.

The select_smoke and pselect_smoke test can fail if STDIN has data ready
to be read. The easiest way to see the failure is to type on the command
line while running the tests.

To avoid this, allow the return value to be 2 or 3 and check which fds
are ready to be read.

Change-Id: Iafba332c5f3ed1943e3d34501f123dd45f06a8c4