add/remove css-classes should be faster

(regex instead of parse/deparse) with the benefit of maintaining
textual ordering also helper add-css-classes and remove-css-classes
have been moved here from ucwb
debugged / better testing of add-css-class
order of classes added by add-class now matches textual ordering, so fix broken test
make %enstream do its job at run time instead of compile time
fixed warnings that were coming from nested %enstream expansions

 * fixed it so nesting will work - robustness / composability
 * removed the nesting - it was uneeded, but should have worked
 * fixed evaluation rules that were befouling the stream argument
   to with-*-snippet
Dont entity escape script content in html-compatibility-mode re ADWolf:#1197 (2)