Merge branch 'mh/abspath'

* mh/abspath:
  t0060: split absolute path test in two to exercise some of it on Windows
  t0060: verify that real_path() removes extra slashes
  real_path(): properly handle nonexistent top-level paths
  t0060: verify that real_path() works correctly with absolute paths
  real_path(): reject the empty string
  t0060: verify that real_path() fails if passed the empty string
  absolute_path(): reject the empty string
  t0060: verify that absolute_path() fails if passed the empty string
  t0060: move tests of real_path() from t0000 to here