[views] extend HTMLStream API to be able to change doctype / xmldecl
When generating RDFa (for instance), the doctype must be :
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN"
"http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd">
This changeset adds a ``set_doctype()`` method on request objects to allow
such changes during page generation.
# copyright %(year)s %(author)s, all rights reserved.# contact %(author-web-site)s -- mailto:%(author-email)s#%(long-license)s"""%(distname)s views/forms/actions/components for web ui"""