add psi-set-demand-value function
add psi-set-demand-value function

This is added to abstract away the representation. psi-get-demand-value is also required
but not for now.

ruiting/opencog,ruiting/opencog,ruiting/opencog,AmeBel/opencog,AmeBel/opencog,andre-senna/opencog,inflector/opencog,misgeatgit/opencog,shujingke/opencog,AmeBel/opencog,yantrabuddhi/opencog,shujingke/opencog,misgeatgit/opencog,ruiting/opencog,shujingke/opencog,ruiting/opencog,andre-senna/opencog,yantrabuddhi/opencog,ruiting/opencog,inflector/opencog,misgeatgit/opencog,inflector/opencog,misgeatgit/opencog,andre-senna/opencog,misgeatgit/opencog,inflector/opencog,inflector/opencog,yantrabuddhi/opencog,misgeatgit/opencog,andre-senna/opencog,inflector/opencog,ruiting/opencog,AmeBel/opencog,shujingke/opencog,misgeatgit/opencog,andre-senna/opencog,misgeatgit/opencog,yantrabuddhi/opencog,shujingke/opencog,misgeatgit/opencog,yantrabuddhi/opencog,AmeBel/opencog,andre-senna/opencog,andre-senna/opencog,yantrabuddhi/opencog,AmeBel/opencog,shujingke/opencog,inflector/opencog,AmeBel/opencog,shujingke/opencog,yantrabuddhi/opencog,inflector/opencog