provide afs_osi_TimedSleep

provide afs_osi_TimedSleep

this interface works how osi_Wait *should*, except on some platforms Wait
appears to wake up all waiters(!) by using a single wait channel in the
backend. rather than change that and risk problems, introduce an interface
using the same system of events we use for osi_Sleep

Change-Id: Ic91726b138bd2512282896ec48c542063ef000cf
Reviewed-on: http://gerrit.openafs.org/1233
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>