Moved ignored Exception#backtrace example to where it belongs.
Renamed version spec files to respect the *_spec.rb scheme.

This also makes them easier to ignore if an implementation cannot parse
the file by excluding it in the .mspec configuration file. Fixes #300.

One way to check for these misnamed files is
$ find . -name '*.rb' | egrep -v '_spec\.rb$|shared|fixture'