Cell: added some functions to do expensive operations cell arrays

They are the equivalent of cellfun(@(x, y){x <op> y}, array1, array2) and similar

Signed-off-by: Nicola Vigano <nicola.vigano@esrf.fr>

git-svn-id: https://svn.code.sf.net/p/dct/code/trunk@661 4c865b51-4357-4376-afb4-474e03ccb993