Check comparisons for very negative numbers as well.

Merged from patch by @sebastianmika.
Applies to Draft4 as well.
Added the json-schema ruby gem to the list of libraries using the test suite
Merge pull request #63 from iainbeeston/patch-1

Added the json-schema ruby gem to the list of libraries using the test suite
Merge remote-tracking branch 'upstream/develop' into jsck