bugfix - slightly more careful approach to renaming channels in case of duplicate labels. The previous approach led to a problem in my example of BTI-4D + EEG data (both had A1 and A2 labels).

git-svn-id: svn+ssh://svn.fcdonders.nl/home/svnroot/fieldtrip/trunk@9832 0cf7c7f0-3615-4144-b4e6-68da3bce3cd0