Commit e4b96fa introduced a nice fix that checks floating point numbers for normality and emits "null" if they aren't.

This is a good thing, however some libm implementations (e.g. the one I have available for my microchip PIC) don't implement the functions fpclassify() & isnormal() which are used in this check. For our local use of cJSON, I've folded in an implementation of these methods from the JuliaLang/openlibm project. I'm not sure if there is a good way to get this back into the trunk.

Any thoughts?