fix minor cython c string compile error
fix minor cython c string compile error

rTreutlein/atomspace,AmeBel/atomspace,rTreutlein/atomspace,AmeBel/atomspace,AmeBel/atomspace,AmeBel/atomspace,rTreutlein/atomspace,rTreutlein/atomspace,rTreutlein/atomspace,AmeBel/atomspace