Added struct tw_message.
Continuing with the rollbackable printing...

Not quite there yet, though.
Checking ret value of vsnprintf().
Rollback-aware output is coming along.

Added the tw_kp_grab_output_buffer() function and I think the
tw_output() function is finished.  Now I need to insert the printing
and reclamation (at GVT) or the reclamation due to an event being
cancelled.
Just reformatting so the changes will be clear.
Lots of changes.  Getting close.
Good enough for tonight.  It appears to work.
More prints than net events...

Trying to track it down.  Maybe events are being run after the
endtime???
Not done.  Just checking in.

I think I need to find more places to free the output messages.  Look
into event_cancel and friends.
Removed unnecessary field from tw_event.
Seems to be functioning correctly.  Need review from Chris.
Just a nice touch.
Just whitespace changes.
More whitespace changes.
Put a tw_ on the front of free_output_messages().
Making all output format the same.
Merge branch 'LP-printf'

This adds the API-level function tw_output() into ROSS.  This is a
rollback-aware printing mechanism, i.e. if the event gets undone (cancel,
rollback, etc.) then the print doesn't happen.  Minimal performance impact
(based on minimal testing... :) if you don't use it so it shouldn't hurt.