Add CallExpr._fields declaration
Add CallExpr._fields declaration

NodeVisitor.generic_visit() doesn't handle "list of list" fields, so
'_fields' must be explicitly set for CallExpr so 'args' and
'keywords' don't get skipped.

* dpy/compiler/dast.py(CallExpr._fields): New field.

sghosh1991/distalgo,sghosh1991/distalgo,mayli/DistAlgo,mayli/DistAlgo