bugfix - read spm/canonical files without requiring them to be accompanied with surface data, see http://bugzilla.fcdonders.nl/show_bug.cgi?id=2359#c3


git-svn-id: svn+ssh://svn.fcdonders.nl/home/svnroot/fieldtrip/trunk@8738 0cf7c7f0-3615-4144-b4e6-68da3bce3cd0