Always pass a sha1 for the initial parent so that git-fast-import doesn't think
it's creating a new branch from itself. It's a sensible error in general but
in the case of incremental imports we have to apply force :)
Reduce the number of false "merges" by skipping "branch from" entries in the integrated output as well as by ignoring integrations of future (newer) changes.
Added a disk-cache p4 output so debugging imports is faster.
Added --known-branches commandline option for pre-defining branches.
Various other fixes...
Make it possible to specify the p4 changes to import through a text file (for debugging) and made various improvements to the branch/merge heuristic detection.