fix fuse impl_c a.k.a. blackmatch

[zooko]

Thomas Delaet contributed a patch to make fuse impl_c a.k.a. blackmatch work:

​http://allmydata.org/pipermail/tahoe-dev/2009-September/002923.html

I've downloaded his patch from that email and attached it to this ticket. Please review and apply!

[francois]

I've just tested this patch on latest trunk and it really does make the blackmatch implementation work again, so it should be included in the next Tahoe release.

The initial breakage was due to this patch:

Sat Jul 18 00:15:49 CEST 2009  Brian Warner <warner@lothar.com>
  * rename NewDirectoryNode to DirectoryNode, NewDirectoryURI to DirectoryURI

The test in the parsing of the '--root-uri' option is commented by the initial patch and I don't really see why because the test worked during my tests. What do you think about keeping it uncommented ? I'll attach a new patch with this modification.

        # test the uri for structural validity:
        try:
            DirectoryURI.init_from_string(root_uri)
        except:
            raise usage.error('root-uri must be a valid directory uri (not %r)' % (root_uri,))

[warner]

keeping the DirectoryURI.init_from_string(root_uri) test is probably ok. I'd like to reduce the use of things like DirectoryURI in the future, but it's probably ok for the near-term.

Sorry about breaking that.. I grepped through src/ for users of those symbols, but I didn't think to grep through misc/ too.. I'd assumed that everything there was speaking webapi rather than importing tahoe code directly.

[zooko]

fixed by eb9358ff6de5cd23