Martin von Zweigbergk <martinvonz@google.com> [Thu, 22 Jan 2015 17:00:54 -0800] rev 23998
trydiff: collect header-writing in one place
This is the first step towards simplifying the big loop in
trydiff(). This will make both the header code and the non-header code
clearer, and it prepares for further simplification of the many nested
if-statements in the body of the loop.