Issue 1823: fix handling of initial alt Codabar char, and improve tests

git-svn-id: http://zxing.googlecode.com/svn/trunk@2996 59b500cc-1b3d-0410-9834-0bbf25fbcc57
Suppress ignorable unchecked cast warning

git-svn-id: http://zxing.googlecode.com/svn/trunk@2997 59b500cc-1b3d-0410-9834-0bbf25fbcc57