t0060: sidestep surprising path mangling results on Windows

t0060: sidestep surprising path mangling results on Windows

When an MSYS program (such as the bash that drives the test suite)
invokes git on Windows, absolute Unix style paths are transformed into
Windows native absolute paths (drive letter form). However, this
transformation also includes some simplifications that are not just
straight-forward textual substitutions:

- When the path ends in "/.", then the dot is stripped, but not the
  directory separator.

- When the path contains "..", then it is optimized away if possible,
  e.g., "/c/dir/foo/../bar" becomes "c:/dir/bar".

These additional transformations violate the assumptions of some
submodule path tests. We can avoid them when the input is already a
Windows native path, because then MSYS leaves the path unmolested.

Convert the uses of $PWD to $(pwd); the latter returns a native Windows
path.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>