Fix Python 3 port in hex_char_dump()
Don’t use assertIsNotNone(), not present in Python 2.6

It was only added in 2.7.
More fixes for sorting items from dictionaries
Another relative import fix
Meant to be a byte string of unknown encoding in this case
Add test for biffh.hex_char_dump()
Add more tests for xlrd.formula
Test reading workbook with ragged rows
Merge branch 'py3-native' into py2.6

Conflicts:
	xlrd/formula.py