Merge branch 'windows-bugs' into 'master'

Check for both os.path.sep and os.path.altsep

*Description of changes*

When normalizing paths, we want to handle the following cases:

- Someone is using a Windows-style path on Windows
- Someone is using a Unix style path on Unix
- Someone is using a Unix style path on Windows

os.path.sep will handle the native directory separator character while os.path.altsep (when set) will handle alternate separators. Further,  os.path.abspath does the right thing on Windows when handed a Unix-style path.

*Related to:*  #175

See merge request !81