[br] detect mutation errors in dates such as:
     "D'ar pemp eus ar miz" -> "D'ar bemp eus ar miz"


git-svn-id: https://languagetool.svn.sourceforge.net/svnroot/languagetool/trunk/languagetool@9419 2fe6a88b-1217-0410-b804-ba6ed01314b8