CSSTidy Code

- Updated French translation

- Some browsers don't send the $_SERVER['HTTP_ACCEPT_LANGUAGE'], so I added a 'isset' otherwise a PHP Notice message and Warning will be showed if $_SERVER['HTTP_ACCEPT_LANGUAGE'] is not set.

Also made DOCTYPEs selective since XHTML 1.1 should only be included if served as XML.

- Added content negotiation to serve XHTML 1.1 as application/xhtml+xml where accepted (no need to change DOM, so JS can work ok too)

Added html style (same as body style) for the sake of true XHTML

- Fix small error of "URL window" to "URL bar"

- Copy to clipboard for Firefox

- Small grammatical clarification in English translation re: CSS validator

- separated German from English to be consistent
- removed trailing ?>
- added entry (in English) for each language re: clipboard in Firefox
- added note about orphaned array slots
- changed test for languages to in_array in order to be more maintainable in the future with additional languages

- Small XHTML 1.0 Strict formatting fix
- Added option in Firefox to copy to clipboard (depends on having a preference set) and added a warning about security concern when not enabled

Extra documentation for CSSTidy testing suite.