bound.

When a Yield() node is visited, assign to the generator attribute of
the scope, not the visitor.

Fix bug in handling of statements like "l[x:y] = 2".  The visitor was
treating this as assignments to l, x, and y!

(Hard to believe these were never handled before)

Add misc.mangle() that mangles based on the rules in compile.c.
XXX Need to test the corner cases

Update CodeGenerator with a class_name attribute bound to None.  If a
particular instance is created within a class scope, the instance's
class_name is bound to that class's name.

Add mangle() method to CodeGenerator that mangles if the class_name
has a class_name in it.

Modify the FunctionCodeGenerator family to handle an extra argument--
the class_name.

Wrap all name ops and attrnames in calls to self.mangle()

Evan Simpson's fix.  And his explanation:

    If you defined two nested functions in a row that refer to the
    same non-global variable, the second one will be generated as
    though the variable were global.

Fixes last bug found with test_scope.py.

XXX Still doesn't work right for classes
XXX Still doesn't do sufficient error checking

Fix func arg processing to handle args in tuples.
In test code, skip names beginning with '.'.

Add mangling support
Add get_children() and add_child() methods to Scope
Skip nodes when If test is a false constant
Add test code that checks results against symtable module