Fix module names for "register" implementation

When compiling with "register" implementation, we found that modules names only contains file names.
Ex :
  src/common/filter.js -> System.register("filter")

In contrario, [karma-runner/karma-traceur-preprocessor] produce the exepcted result:

  src/common/filter.js -> System.register("src/common/filter")

This tiny pull request fix this, without changing the current behaviour of others implementaions ('amd', 'commonjs')