- The fat binaries for the ffi gem do not support Ruby 1.9.3, hence
  testing on this version on Windows makes no sense.
- To set Ruby version 2.0.0, the micro version also needs to be set.

The existing default is not needed, since ENV is always used as a base
for the local environment.

- Use inject on all versions of Ruby, not need to make a distinction
  here.
- Clean up overrides in WindowsEnvironmentVariables
- Override to_h in WindowsEnvironmentVariables so it correctly upcases
  ENV values.

SpawnProcess should work without specifying these, and there are no
specs that essentially override these defaults.

Instead of setting up or using a shell script, just use Ruby with a
script on the command line.

This splits the specs in a Unix and Windows versions, just like for the
specs for commands with spaces.

This method basically returns one of the initializer arguments so makes
little sense.