Fixed deadlocking error.

Diagnosed a strange deadlocking error where if an invalid values in double scalers error was encountered by numpy during the kruskal wallis calculations, the interpreter would just hang rather than report an error. This SO post describes the error: http://stackoverflow.com/questions/11670404/mod-wsgi-hangs-on-runtimewarning-divide-by-zero

A simple check for 0 divisor suffices in this case, but in other cases this may be hard to detect. Some global resolution to this kind of issue would be nice.
Modified sort_by_pvals

Modified sort_by_pvals so that it would assign nans a +inf value for purposes of comparison. If this was not implemented sorting of pvals containing nans would leave blocks of sorted values between nan values.
Modified mutliple scripts to prevent test failure

Caught several test failures and modified scripts to prevent them including OTU significance and core_diversity_analyses.py
Began modification of otu_gradient_correlation.py to conform to guidelines released by Cathy.