Short circuit binary operators about copperhead HOT 1 OPEN

The main problem with fixing this has to do with expression flattening: compound expressions are all flattened in the front end of the compiler, so this:
if y or sum(x) > 1 :
pass

becomes
e0 = sum(x)
e1 = e0 > 1
if y or e1:
pass

Later on, e1 will be evaluated before we get to the conditional, so the short-circuiting behavior of "or" is not respected.

To fix this, we're going to need to lift all expressions in conditionals into lambdas:
if y or (lambda:sum(x) > 1)():
pass

Before lambda lifting occurs. Arguments to these lambdas occur via closures.

Doing this will require fixing issue #4 (entry point model).

from copperhead.