os: the WNOHANG, etc constants are weird and non-portable

[bradfitz]

Problems with the bits in *os.Process Wait(options int)

1) they're non-portable
2) they're a mix of syscall bit numberspace and Go-assigned numbers (1 << 20 for
os.WRUSAGE)

We should clean this up somehow:

a) remove the options parameter to Wait
b) keep the options parameter, but document the bits as all Go-defined portable bits
(like FileMode)
c) document that they're all syscall bits and pass them along, but don't provide alias.
force callers to use syscall.WNOHANG, etc.  that leaves WRUSAGE, but we could just
always return that, and remove WRUSAGE.

d) ???

[bradfitz]

Comment 1:

Status changed to Duplicate.

Merged into issue #2949.