revsets: huge speedups for fromsvn and svnrev I have a hgsubversion repo that contains over 300,000 commits. In that repo, this patch improves performance as follows: hg --time log -r 'first(fromsvn())' Before: 40.3 sec After: 0.8 sec hg --time log -r 'svnrev(350000)' Before: 40.3 sec After: 0.1 sec Note: the performance of these revset implementations is very sensitive to doing as little work as possible per line of the rev_map file. I originally attempted to hide the file format details by hoisting the parsing of each line up into RevMap.readmapfile, but the current less abstract code is dramatically (10x or more) faster. If the revmap file is missing, we error out and print a message describing what to do.

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