Support non-commercial usage of schema.org/Offer - RDF(S) patch

Hello:

Following the great discussion that began with
http://lists.w3.org/Archives/Public/public-vocabs/2013Sep/0088.html I've
put together a patch that addresses the bulk of the overly-commercial
definitions in the current iteration of schema.org.

Apologies if the git diff format is inappropriate; I've been mirroring
schema.org in a local git repo as the core pages do not appear to be
available in the w3 webschema mercurial repo.

Please let me know if I should generate diffs for the individual type /
property pages as well, rather than just
http://schema.org/docs/schema_org_rdfa.html