Fix bug involving autoclose and inline elements in strict <blockquote>.
The newest autoclose code uses the elements property in whether or not an
element should be closed by a particular tag. The heuristic is simple; if
the element doesn't allow that tag as a child, it closes the parent
container. This doesn't work, however, with <blockquote>, which while not
allowing inline styles under Strict doctypes, requires them to be passed
through MakeWellFormed.
The fix was to transition MakeWellFormed to call a method to retrieve the
elements, and then have StrictBlockquote implement a special version of
this method. Future versions of HTML Purifier may be more flexible in this
regard--further study of the HTML5 specification is required.
Signed-off-by: Edward Z. Yang <edwardzyang@thewritingpot.com>