FIX tests for windows

[srsbiz]

Summary of changes for tests to work in windows environments:

• normalized paths where possible for assertions
• use DIRECTORY_SEPARATOR inside paths where normalization is not possible
• prepend php to command line tests
• use NUL instead of /dev/null for error output in command line tests

[DerManoMann]

Looking ok to me. Happy to merge if you at least update composer.json

[DerManoMann]

I think there is still an opportunity to use short functions but I feel this will do for now.
v6 will bring some changes to tbe Util class, maybe that is the time to do some more cleanup here.

[DerManoMann]

Thanks @srsbiz