Provide a log handler to log errors.

[Steelskin]

Original issue 33 created by thakis@google.com on 2011-12-09T03:58:01.000Z:

#include <iostream> introduces static initializers, see http://crbug.com/94794

open-vcdiff logs through cerr. If open-vcdiff must log, it should use fprintf(stderr, ...) – or, probably better, provide a log handler that embedders could override to do what they please.

[Steelskin]

Nothing very important in the old comments.
Increasing priority, this would allow open-vcdiff to work nicer with chromium for instance.

[nico]

Note that Chromium hacked around this: https://code.google.com/p/open-vcdiff/issues/detail?id=33#c11

It'd still be nice if that hack wasn't needed though.