Rationalise Parser PHP & HTML syntax mode handling to renderer only.

This patch corrects the problems with the previously (reversed) patch
"remove htmlok and phpok tests from Doku_Handler".

The handler will now write php, phpblock, html & htmlblock instructions
and let the renderer decide how these instructions should be processed.

The xhtml renderer will follow the "phpok" and "htmlok" config settings.
If these settings are turned off the any instructions will be rendered as
code with php or html syntax highlighting (as appropriate).

darcs-hash:20080213024941-d26fc-ec485362803e63a2d949dad5c23e17db939e6ced.gz