Support for PREBUILT_ILLUMOS, and optional /tmp/debug.$$ output.

*** 6,14 ****
--- 6,19 ----
  # the top level of your checkout and publish there instead
  # of the URI specified above.
  #
  #PKGSRVR=file:///$MYDIR/../tmp.repo/
  
+ # Uncommenting this line will use a pre-built illumos-omnios, instead of having
+ # us build it.  NOTE: A build of illumos-omnios can be launched concurrently in
+ # conjunction with setting this variable. See functions.sh:wait_for_prebuilt().
+ #PREBUILT_ILLUMOS=$HOME/build/prebuild
+ 
  # These two should be uncommented and set to specific git changeset IDs
  # if illumos-kvm and illumos-kvm-cmd get too far ahead of illumos-{gate,omnios}.
  #KVM_ROLLBACK=a8ea37e8deb99265682c66c23f787f704e77fb91
  #KVM_CMD_ROLLBACK=1c6181be55d1cadc4426069960688307a6083131