bugfix: RemoveAll

[yearnfar]

when i RemoveAll lib directory, it also Removed libs directory

[CLAassistant]

All committers have signed the CLA.

[jxsl13]

and you need to press on the cla bot signed yet button.

[jxsl13]

merge pls :D

[mbertschler]

@yearnfar I don't fully understand what the problem is, you want the directory to be also removed but it currently isn't?

Can you please add a test for this problem?

[jxsl13]

you add a trailing filepath separator in order to prevent other directories starting with the same prefix from being deleted as well as the one you actually want to delete.

General thought:
A lot of this stuff should not really rely on strings.HasPrefix but rather filepath.Rel(pathA,pathB string) (relPath string, err error)

For MemMapFs this should suffice as iirc it does add a trailing slash at the end of a directory name.