Tweaked Makefile for better Windows compatibility

Windows has trouble with dot slash notation, so `npm test` had trouble running in Command Prompt and Cygwin. I was able to get the make tasks to run by shortening the paths to just `mocha`, which NPM is able to resolve fairly well.

There's still a minor failing test in Windows, but at least `npm test` is able to run now.

    $ npm test

    > mocha@1.9.0 test c:\Documents and Settings\apenneba\Desktop\src\mocha
    > make test-all

    mocha \
                    --reporter dot \
                    --ui bdd \
                    test/acceptance/interfaces/bdd
    mocha \
                    --reporter dot \
                    --ui tdd \
                    test/acceptance/interfaces/tdd
    mocha \
                    --reporter dot \
                    --ui qunit \
                    test/acceptance/interfaces/qunit
    mocha \
                    --reporter dot \
                    --ui exports \
                    test/acceptance/interfaces/exports
    mocha \
                    --reporter dot \
                    test/acceptance/*.js \
                    test/*.js

      ..................................................................
      .......................................

      × 1 of 105 tests failed:

      1) fs.readFile() when the file exists should succeed:
         Error: ENOENT, open 'c:\tmp\mocha'



    make: *** [test-unit] Error 1
    npm ERR! Test failed.  See above for more details.
    npm ERR! not ok code 0