convert: add a mode where mercurial_sink skips empty revisions. The getchanges function of some converter_source classes can return some false positives. I.e. they sometimes claim that a file "foo" was changed in some revision, even though its contents are still the same. convert_svn is particularly bad, but I think this can also happen with convert_cvs and, at least in theory, with mercurial_source. For regular conversions this is not really a problem - as long as getfile returns the right contents, we'll get a converted revision with the right contents. But when we use --filemap, this could lead to superfluous revisions being converted. Instead of fixing every converter_source, I decided to change mercurial_sink to work around this problem. When --filemap is used, we're interested only in revisions that touch some specific files. If a revision doesn't change any of these files, then we're not interested in it (at least for revisions with a single parent; merges are special). For mercurial_sink, we abuse this property and rollback a commit if the manifest text hasn't changed. This avoids duplicating the logic from localrepo.filecommit to detect unchanged files.

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% initial svn import

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Adding         t/a

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Committed revision 1.

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% update svn repository

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A    t2/a

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Checked out revision 1.

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A         b

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Sending        a

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Adding         b

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Transmitting file data ..

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Committed revision 2.

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% convert to hg once

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assuming destination trunk-hg

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initializing destination trunk-hg repository

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scanning source...

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sorting...

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converting...

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1 init

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0 changea

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% update svn repository again

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Sending        a

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Sending        b

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Transmitting file data ..

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Committed revision 3.

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% test incremental conversion

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assuming destination trunk-hg

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destination trunk-hg is a Mercurial repository

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scanning source...

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sorting...

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converting...

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0 changeb