Fixed: CPNumberFormatter minimum and maximum wrong encoding when set to nil

Previously, a decoded CPNumberFormatter was converting the minimum and maximum values to 0 if they were set to nil. This was causing unexpected behavior when creating a CPNumberFormatter from a xib. This patch actually decodes _minimum and _maximum values as objects to preserve nil.

Test added in Foundation/CPNumberFormatter.j
Merge branch 'master' of https://github.com/cappuccino/cappuccino