Attempts to clean up generated HTML.

Attempts to clean up generated HTML.

WikiTransform::SetHTMLMode():

  Eliminate the $tagtype argument, since somewhere along the line it
had lost all meaning.

  Check when pushing nested elements that the top-level element is of
a type which can contain other block-level elements. Elements of type
<p>, and <pre>, among others, are not allowed to contain other
block-level elements.

wtm_list_dl:
  Fix bug (which manifested itself only with non-empty <dt>s).

Some remaining problems which perhaps should be addressed:

Wtm_title_search, wtm_fulltext_search, wtm_mostpopular as well
as some of the the magic phpwiki: links (the ones which generate
forms) all generate some sort of block-level HTML element (either
<form>s or <dl>s.)  As noted above, these are not allowed within
<p> elements (and others).

Bold/italics:    __Bold ''BoldItalic__ Italic''
 ... it's contrived, but it will generate improperly nested HTML.

git-svn-id: svn://svn.code.sf.net/p/phpwiki/code/trunk@456 96ab9672-09ca-45d6-a79d-3d69d39ca109