Remove mock when not needed
FileAssert#hasParent should not fail using absolute path [Issue #193]

  File f = new File("./some/test");

  //fail
  File absolute = new File(f.getAbsolutePath());
  assertThat(f).hasParent(absolute.getParent());

It was failing because parent comparison was done between absolute
and relative representation.
It now always use the canonical form.
Merge pull request #195 from jcgay/issue-193

FileAssert#hasParent should not fail using absolute path