[Cosmo-dev] changes to atom collection update

[Brian Moseley]

i had to make some plumbing changes to atom updates of collection
details. because we're now using PUT, the servlet api doesn't
automatically parse form-encoded request content and provide it as
request parameters. therefore, since we have to manually process the
request content, i decided to be symmetrical with how we represent
subscriptions and preferences, so i created a trivial xhtml
microformat for collection details. find more info at
<http://chandlerproject.org/Projects/CosmoMicroformats#Collection%20Details>.
ps: this means that the content type of these PUTs must now be
application/xhtml+xml.