Accept unicode with ascii code points from read callback on python 2
Test byte strings returned from read callback on python 2
Python 2.4 and 2.5 compatibility
Use PyByteStr_AsStringAndSize macro for dryness
Add PyByteStr_Check macro for dryness and uniformity
Merge pull request #139 from p-push/unicode-read-function-python-2

Accept Unicode with ascii code points from read function on python 2