enhancement - it turns out refmag and refgrad for BTi can be distinguished based on labels. This is done for grad.chantype but not for hdr.chantype resulting in the two being different. I copied a bit of code to fix that.

git-svn-id: svn+ssh://svn.fcdonders.nl/home/svnroot/fieldtrip/trunk@9869 0cf7c7f0-3615-4144-b4e6-68da3bce3cd0