Cleanup and fix isConstExpr to return true for all atomic node types.
Cleanup and fix isConstExpr to return true for all atomic node types.

russpowers/Nim,jfhg/Nim,singularperturbation/Nim,jfhg/Nim,singularperturbation/Nim,russpowers/Nim,dom96/Nim,tulayang/Nim,singularperturbation/Nim,tulayang/Nim,tulayang/Nim,haiodo/Nim,mbaulch/Nim,mbaulch/Nim,haiodo/Nim,haiodo/Nim,russpowers/Nim,singularperturbation/Nim,haiodo/Nim,mbaulch/Nim,mbaulch/Nim,russpowers/Nim,dom96/Nim,russpowers/Nim,singularperturbation/Nim,jfhg/Nim,tulayang/Nim,mbaulch/Nim,jfhg/Nim,mbaulch/Nim,tulayang/Nim,dom96/Nim,jfhg/Nim,jfhg/Nim,haiodo/Nim,dom96/Nim,tulayang/Nim,mbaulch/Nim,russpowers/Nim,russpowers/Nim,dom96/Nim,dom96/Nim,dom96/Nim,haiodo/Nim,singularperturbation/Nim,haiodo/Nim,jfhg/Nim,singularperturbation/Nim