1.5.2.  The compiler generates code for the version of the interpreter
it is run under.

ast.py:
    Print and Printnl add dest attr for extended print
    new node AugAssign for augmented assignments
    new nodes ListComp, ListCompFor, and ListCompIf for list
        comprehensions

pyassem.py:
    add work around for string-Unicode comparison raising UnicodeError
        on comparison of two objects in code object's const table

pycodegen.py:
    define VERSION, the Python major version number
    get magic number using imp.get_magic() instead of hard coding
    implement list comprehensions, extended print, and augmented
        assignment; augmented assignment uses Delegator classes (see
        doc string)
    fix import and tuple unpacking for 1.5.2

transformer.py:
    various changes to support new 2.0 grammar and old 1.5 grammar
    add debug_tree helper than converts and symbol and token numbers
    to their names