bugfix - fixed regression problem in test_bug70, which was due to the estimate of cfg.grid.unit being incorrect for a single dipole position. I changed it such that it only tries to determine it on the grid if there are more than 10 dipole positions, otherwise it uses sens.unit or vol.unit


git-svn-id: svn+ssh://svn.fcdonders.nl/home/svnroot/fieldtrip/trunk@8705 0cf7c7f0-3615-4144-b4e6-68da3bce3cd0