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.

changeset = 'changeset:   {rev}:{node|short}\n{branches}{tags}{parents}user:        {author}\ndate:        {date|date}\nsummary:     {desc|firstline}\n\n'
changeset_quiet = '{rev}:{node|short}\n'
changeset_verbose = 'changeset:   {rev}:{node|short}\n{branches}{tags}{parents}{manifest}user:        {author}\ndate:        {date|date}\n{files}{file_adds}{file_dels}{file_copies}description:\n{desc|strip}\n\n\n'
changeset_debug = 'changeset:   {rev}:{node}\n{branches}{tags}{parents}{manifest}user:        {author}\ndate:        {date|date}\n{files}{file_adds}{file_dels}{file_copies}{extras}description:\n{desc|strip}\n\n\n'
start_files = 'files:      '
file = ' {file}'
end_files = '\n'
start_file_adds = 'files+:     '
file_add = ' {file_add}'
end_file_adds = '\n'
start_file_dels = 'files-:     '
file_del = ' {file_del}'
end_file_dels = '\n'
start_file_copies = 'copies:     '
file_copy = ' {name} ({source})'
end_file_copies = '\n'
parent = 'parent:      {rev}:{node|formatnode}\n'
manifest = 'manifest:    {rev}:{node}\n'
branch = 'branch:      {branch}\n'
tag = 'tag:         {tag}\n'
extra = 'extra:       {key}={value|stringescape}\n'