First pass at better signal handling:

First pass at better signal handling:

  -- Add afs_osi_SleepSig, which returns EINTR when interrupted by signal.
  -- Similar CV_WAIT_SIG for Rx code.
  -- Implement afs_osi_SleepSig and CV_WAIT_SIG for Linux, Solaris.
  -- Use afs_osi_SleepSig in afs_{UFS,Mem}Read, allowing user to interrupt
     an AFS read if it's being handled by background daemon.
  -- Balance the number of open & close braces in CV_TIMEDWAIT macros,
     even though noone uses them.
  -- Untangle parts of the macro forest by moving some of the Rx CV code
     into rx_kmutex.c.