test-require-resolve: use case insensitive compare

The test fixtures directory is derived from the path to the currently
running script, which is itself specified on the command line. That
means that the case of the fixtures dir may not match what the test
expects (when executed on a case-insensitive file system).

PR-URL: https://github.com/iojs/io.js/pull/116
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>