Copy 3.2 builtins and typing stubs to 2.7

No changes yet to 3.2 stubs.
Fixes to 2.7 builtins
Support unicode literals in lexer
Fix triple-quoted unicode literals
Remove obsolete code
Add Python 2 parser mode; parse unicode literals
Make u'foo' same as 'foo' in Python 3 syntax

This corresponds to Python 3.3.
Refactor mypy script
Refactor Python 2 mode setting
Support for Python 2 type checker test cases
Type check unicode literals
Add Python 2 abc stubs
Copy Python 3 re stub to Python 2
Fixes to Python 2 builtins
Fixes to Python 2 stubs
Refactor Python 2.7 builtins stubs
Add long and bytes to Python 2.7 builtins stubs
Support type checking using Python 2 stubs
Install Python 2 stubs