[br] improved disambiguation of word "a" to detect error in:
     *Ur bihan a paotr.* -> "Ur bihan a baotr."


git-svn-id: https://languagetool.svn.sourceforge.net/svnroot/languagetool/trunk/languagetool@9798 2fe6a88b-1217-0410-b804-ba6ed01314b8