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.

#!/usr/bin/env python

__doc__ = """This does HTTP get requests given a host:port and path and returns
a subset of the headers plus the body of the result."""

import httplib, sys
headers = [h.lower() for h in sys.argv[3:]]
conn = httplib.HTTPConnection(sys.argv[1])
conn.request("GET", sys.argv[2])
response = conn.getresponse()
print response.status, response.reason
for h in headers:
    if response.getheader(h, None) is not None:
        print "%s: %s" % (h, response.getheader(h))
print
sys.stdout.write(response.read())