xhtml 6.x-1.1

This release makes xhtml feasible on the drupal6 platform except for #1225954: teaser.js is incompatible with application/xhtml+xml.

• Remove a stray error_log() call.
• Don't ignore template suggestions added by other modules' hook_preprocess_page() implementations. Now appending a template to $variables['template_files'] will both use that suggested template and coerce it into having the proper <?xml?> declaration, etc.
• Fix #1225952: Internet Explorer doesn't send text/html in its Accept header