Changed rule for LDPC PUT to be about containment triples

Per recent email discussions [1], it pointed out a rule that wasn't updated
to match recent resolutions.  The idea was really about guiding clients not
to expect to affect triples that are managed by the server, namely the
containment triples (in today's terminology).  So I updated it [2] to
reflect that:

[[
6.5.1 LDP servers SHOULD NOT allow HTTP PUT to update a LDPC's containment
triples.
]]

[1] - http://lists.w3.org/Archives/Public/public-ldp-wg/2014Feb/0076.html
[2] - https://dvcs.w3.org/hg/ldpwg/raw-file/default/ldp.html#ldpc-HTTP_PUT


- Steve Speicher