TST fixed ProjectUtilsTest on OS X

[kmike]

Temp folder can be a symlink on OS X; tests failed for me with this exception:

tests/test_utils_project.py F.

================================================================== FAILURES ===================================================================
_______________________________________________ ProjectUtilsTest.test_data_path_inside_project ________________________________________________

self = <tests.test_utils_project.ProjectUtilsTest testMethod=test_data_path_inside_project>

    def test_data_path_inside_project(self):
        with inside_a_project() as proj_path:
            expected = os.path.join(proj_path, '.scrapy', 'somepath')
>           self.assertEquals(expected, data_path('somepath'))
E           AssertionError: '/var/folders/_5/cbsg50991szfp1r9nwxpx85800[31 chars]path' != '/private/var/folders/_5/cbsg50991szfp1r9nw[39 chars]path'
E           - /var/folders/_5/cbsg50991szfp1r9nwxpx8580000gn/T/tmp_v300tga/.scrapy/somepath
E           + /private/var/folders/_5/cbsg50991szfp1r9nwxpx8580000gn/T/tmp_v300tga/.scrapy/somepath
E           ? ++++++++

This PR fixed that.