Make the choice of diff algorithm configurable by diff API users. The got and gotweb programs keep using Patience diffs which are prettier than Myers. But tog should be as fast as possible since it is being used interactively. If performance of Patience diff gets improved later we can consider switching tog back over to it. ok tracey jamsek

ok tracey

Throwing this into the mix for a while, we can always get rid of it again if it becomes annoying. No objections from stsp@

thanks for all the help massaging this diff

ok tracey

Saves us from doing a malloc/free call for every item on the list. ok op@

ok op@

Instead of internally opening and closing the same commit object over and over again, require callers to pass an open commit object in. Avoids an inherent dependency on the commit object cache for reasonable performance. ok op@

ok op@

ok thomas_adam millert

suggested by millert ok thomas_adam

Need for filtering by path sugggested by kn@ ok naddy@

This commit modifies the GoT main branch to be able to compile it under linux.

Problem noticed by naddy due to failing regress tests at midnight, and then analyzed with additional help from millert. ok naddy