paths: Added trailing slashes and dots tests

As expected these are failing and will need some work to pass.

The issue with lfs_file_open allowing trailing slashes was found by
rob-zeno, and the issue with lfs_mkdir disallowing trailing slashes was
found by XinStellaris, PoppaChubby, pavel-kirienko, inf265, Xywzel,
steverpalmer, and likely others.

Author: geky