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.

#!/bin/sh

cat > abortcommit.py <<EOF
from mercurial import util

def hook(**args):
    raise util.Abort("no commits allowed")

def reposetup(ui, repo):
    repo.ui.setconfig("hooks", "pretxncommit.nocommits", hook)
EOF
abspath=`pwd`/abortcommit.py

echo "[extensions]" >> $HGRCPATH
echo "mq=" >> $HGRCPATH
echo "abortcommit = $abspath" >> $HGRCPATH

hg init foo
cd foo
echo foo > foo
hg add foo

# mq may keep a reference to the repository so __del__ will not be called
# and .hg/journal.dirstate will not be deleted:
hg ci -m foo
hg ci -m foo

exit 0