In preparation of #24723, I would've started a second time of search-and-replacing, but I decided to fix the following duplication and obsoletion upfront:

• extracted internal style sheets from wiki_syntax_detailed_[markdown|textile].html into an external one (wiki_syntax_detailed.css)
• extracted internal style sheets from wiki_syntax_[markdown|textile].html into an external one (wiki_syntax.css)
• removed old, obsoleted and unused 'Content-Style-Type' meta tag

I attach three patches implementing these changes. This patch serial, against current source:/trunk@16171, is produced using git format-patch which makes the individual patches apply-able using "@patch -p1 < 0001-...@".