Fixed a couple of typos in setup script

Made 'sources' a list of string(s), and also fixed a typo.

avoid unnecessary safety temping of function arguments that are builtins or read-only variables (e.g. extension types)

added dump_pos() method to Node class as a quick debugging way to figure out where a node lives in the source code

make refnanny output easier to detect when used outside of doctests, print number of references leaked

fix for refnanny C code in dict iteration: generate all GOTREFs before all coercions before all assignments to properly handle error cases

work around C compiler warnings about unused utility functions by registering the signature with the smallest dependency last

Fixes setup filename in Demos/Makefile.