Pattern matching does not match redis behaviour

[bmerry]

The implementation of KEYS and SCAN uses fnmatch.fnmatch to match the pattern. This has a few problems:

• At a minimum it should use fnmatchcase to avoid being case-insensitive on some OSes.
• It does not support backslash escapes.
• It uses ! instead of ^ for negated
• It seems to handle invalid ranges like [e-a] differently (raises an exception, whereas redis does something unspecified I still need to work out).

It also operates by turning both arguments into native strings using the system default encoding, even though they might not be valid in that encoding.