drop xhtml content-type support (closes #2065651)
* HTMLStream does not care about xml any more
* reqquest.demote_to_html and .xhtml_browser are deprecated
* web config: drop force-html-content-type option
* adjust tests
\.svn
^build$
^dist$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
syntax: regexp
.*/data/database/.*\.sqlite
.*/data/database/.*\.config
.*/data/database/tmpdb.*
.*/data/ldapdb/.*
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/