Fixes issues with security.create_token() and Unicode problems

[gorakhargosh]

bytes, str, unicode, and basestring mean different
things to Python 2.5, 2.6, and 3.x.

Python 2.5

• bytes is not available.
• str is a byte string.
• unicode converts to unicode string.
• basestring exists.

Python 2.6

• bytes is available and maps to str
• str is a byte string.
• unicode converts to unicode string
• basestring exists.

Python 3.x

• bytes is available and does not map to str.
• str maps to the earlier unicode, but unicode has been removed.
• basestring has been removed.
• unicode has been removed

This patch adds portable support for all three versions
of Python by adding a portable types module.
All Unicode handling has been replaced to use the
functions from this module and tests pass.

It introduces these portable types that you can use
in your code:

• bytes where you need byte strings.
• unicode_string where you need unicode strings
• a few other utility functions that hide all the
  complications behind type checking therefore cleaning
  up the code base.
• The function create_token() can now accept a numerical base argument.
• All create_token() usages have been updated to return expected
  hexadecimal string.
• Tests have been added for decimals.
• All create_token() tests pass.
• bytes is a Python 2.6+ type not available
  in Python 2.5. This patch fixes it with a suitable
  replacement.

webapp2 is still small, but it doesn't necessarily mean
we can't use packages. All the existing tests pass
without affecting any existing parent projects.

This patch ensures webapp2 can be easily ported
to Python 3.x in the future as and when required.

Signed-off-by: Gora Khargosh gora.khargosh@gmail.com