* Fix cannot create Windows directory in root
Fixes#20306, a regression bug with `createDir` caused by
`23e0160af283bb0bb573a86145e6c1c792780d49`.
The issue is that, if the path consists only of a drive and a single
directory (e.g. "Y:\nimcache2" in the original issue), then no
directories will be created. This works fine if there are multiple
directories (e.g. "Y:\nimcache2\test").
In the case of "Y:\nimcache2", `omitNext` in `createDir` is `false` on
the last condition in `createDir`. This means that the "nimcache2"
directory will not be created, and no exception will be raised.
Fixed by refactoring to use `parentDirs` iterator instead of iterating
over the string characters. Motivation is reduced code complexity.
Will not test the specific "C:\test" `createDir` case, since there is no
standard Windows drive with write permissions in the root. Creating a
custom drive-mapping to Windows Temp is a non-option. That could mess
up some users running the test.
Added `parentDirs` tests since they are lacking on for POSIX paths.
* Fix `createDir("")` causing error
The change to `createDir` caused `createDir("")` to raise an error,
where it previously didn't. Fixed so `createDir("")` does not fail, and
added test case.
68f92af17c