Ensure that test excercises unique code path

The module source code should be distinct from the previous test to
ensure that the transformation takes place because of the
`shimOverrides` option.
Specify `shimOverrides` via module identifier

AMDClean generates a module "name" for internal use based on each
module's identifier. Users of the library should be able to reference
modules by their identifier (not the internal name).
Fix bug in `shimOverrides` option

Ensure that the expression specified by `shimOverrides` is honored when
a shimmed module exports a Function value.
Merge pull request #58 from jugglinmike/fix-override

Fix override