Updating Freedesktop glob database with new recent one having weights.

Breaking changes:

* Changing expected MIME-Type for .flac extension. audio/flac is now not
  vendor prefixed anymore. Detecting extension for audio/x-flac without
  simplifying will now fail; detect for audio/flac instead.

* Adding xsl to list of prefreferred extensions as xsl is now its
  own MIME-Type with two extensions available; application/xml
  will not return .xsl/.xslt extensions as a result anymore, use
  application/xsl for that. Adding test for new xsl MIME-Type.

Non-breaking changes:

* Fixing expected order of bzip extensions; .bz2 already in preferred
  extensions; no behavior change when using the Mime_Type class to
  detect extension for application/x-bzip.

* Fixing expected order of css extensions; .css already in preferred
  extensions; no behavior change when using the Mime_Type class to
  detect extension for text/css.

* Fixing expected order of gettext translation extensions; .mo already
  in preferred extensions; no behavior change when using the Mime_Type
  class to detect extension for application/x-gettext-translation.

* Adding .gem to the list of extensions for application/tar; no behavior
  change when using the Mime_Type class to detect the extension for
  application/tar as .tar is already in the list of preferred
  extensions.

* Changing expected order of extensions for text/plain; no behavior
  change when detecting extension for text/plain as .txt is already in
  the list of preferred extensions.

* Adding .f4a to the list of extensions for audio/mp4; no behavior
  change when using the Mime_Type class to detect the extension for
  audio/mp4 as .m4a is already in the list of preferred
  extensions.
Updating Freedesktop magic.db with most recent version.

* Re-enabling previously failing tests.
* Re-check and updating comments on previosly failing tests.
Adding tests for webm.