rdoc/rdoc — pull request #287 by tenderlove (2014-01-16 22:03:02+00:00)
Title: return nil unless `other` is comparable.  Fixes #284

Apparently RDoc was relying on `<=>` raising an exception to mean "not comparable" rather than returning nil. This patch returns nil when they are not comparable. Ruby trunk raises an exception due to [this ticket](https://bugs.ruby-lang.org/issues/7688).