Add __lt__ methods for Python 3 compatibility to date.i and money.i.

Python 3 no longer supports __cmp__ methods and requires __lt__ methods
for comparison.  For backward compatibility with Python 2, previously
implemented __cmp__ methods in the .i files are not removed.
Remove leading zeros from integer literals.

Python 3 raises syntax errors for leading zeros in integer literal while
Python 2 interprets them as octal numbers.  Neither is a desired
behavior.
Port Python 2-specific syntax into Python 3-compatible syntax.

Note that the resulting code is intended to be compatible with both
Python 2 and 3.