manifest: skip fastdelta if the change is large In large repos, the existing manifest fastdelta computation (which performs a bisect on the raw manifest for every file that is changing), is excessively slow. This patch makes fastdelta fallback to the normal string delta algorithm if the number of changes is large. On a large repo with a commit of 8000 files, this reduces the commit time by 7 seconds (fastdelta goes from 8 seconds to 1). I tested this change by modifying the function to compare the old and the new values and running the test suite. The only difference is that the pure text-diff algorithm sometimes produces smaller (but functionaly identical) deltatexts than the bisect algorithm.