MFC r266924:

Glibc was switched to the FUTEX_WAIT_BITSET op and CLOCK_REALTIME
flag has been added instead of FUTEX_WAIT to replace the FUTEX_WAIT
logic which needs to do gettimeofday() calls before the futex syscall
to convert the absolute timeout to a relative timeout.
Before this the CLOCK_MONOTONIC used by the FUTEX_WAIT_BITSET op.

When the FUTEX_CLOCK_REALTIME is specified the timeout is an absolute
time, not a relative time. Rework futex_wait to handle this.
On the side fix the futex leak in error case and remove      useless
parentheses.

Properly calculate the timeout for the CLOCK_MONOTONIC case.

Tested by:      Hans Petter Selasky

Approved by:	re (glebius)