The function UGM_CRFcell_NLL.m

The function UGM_CRFcell_NLL.m, as well as example_UGM_OCR.m which is a
demo showing how to apply UGM to data sets where different examples have
different numbers of nodes and/or different graph structures, which was
by far the most requested feature to add to UGM.
Fixed an indexing bug in the message-passing.

Fixed an indexing bug in the message-passing.