fixes issues with lists, as well as some assertions (issues 107/108/110)

 * allow list items to have the value attribute!
 * epub_nordic_127: check all ancestors for frontmatter or backmatter fixes #107
 * invert assertion tpb143. fixes #108
 * pf:numeric-alpha-to-decimal only works for single characters. Added implementation for multiple characters. fixes #110
   * added test for ordered list items using characters where multiple characters are present
 * dtbook-legacy-fix.xsl: always set track:Guidelines to 2011-2
Merge branch 'issue-107-108-110'