handle del inside function definition

[Hanaasagi]

It will resolve #428.

a = 1

def test():
    a = 2
    del a
    print(a)

test()

handleNodeLoad will always search the name a from function scope to module scope, even if we defined a same name in function and then delete it. We need to remember the name we deleted. Because of name shadowing, Python will not search the outer scope.

[Hanaasagi]

Know little about PyPy, it's behavior is different from Python :joy:

[asottile]

looks like new versions of pypy have different offsets, I'll make a PR to fix that -- should be unrelated to your change here 👍

[Hanaasagi]

Hello, are there any questions about this PR?