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.

adding bar
adding foo
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
% start imerge
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
U foo
foo
bar
bar
bar
% status -v
merging e6da46716401 and 30d266f502e7
U foo (foo2)
% next
foo
% merge next
merging foo and foo2
all conflicts resolved
% unresolve
% merge foo
merging foo and foo2
all conflicts resolved
% save
% load
2 files updated, 0 files merged, 1 files removed, 0 files unresolved
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
R foo
all conflicts resolved
foo
changeset:   3:fa9a6defdcaf
tag:         tip
parent:      2:e6da46716401
parent:      1:30d266f502e7
user:        test
date:        Thu Jan 01 00:00:03 1970 +0000
files:       foo foo2
description:
merged


% nothing to merge -- tip
abort: there is nothing to merge
2 files updated, 0 files merged, 1 files removed, 0 files unresolved
% nothing to merge
abort: there is nothing to merge - use "hg update" instead