Re: Documentation/MyFirstObjectWalk: add #include "trace.h" to use trace_printf()

Hi! I pulled down walken.c from https://github.com/nasamuffin/git/tree/revwalk and was able to fix the broken code. I also fixed Documentation/MyFirstObjectWalk.txt and have accordingly pushed all the changes to my fork of git:

https://github.com/vinayakdsci/git/tree/revwalk-fixed

I had to remove init_walken_defaults() as I could not trace the function init_grep_defaults() which I think has been removed since you wrote the tutorial. I also didn't find a mention of init_grep_defaults() in the tutorial, so maybe that is alright. Also, struct list_objects_filter_options is included inside of rev_info, so I don't think it requires initialisation any more.

It would be great if you are able to use this branch to rewrite your own!

Thanks a lot! Vinayak