* Fix Rename-Item to allow Unix globbing patterns in -Literal paths (#2799)
In the process of normalizing a relative path, PowerShell checks to see
see if the path exists, which it does by invoking
Directory.EnumerateFiles(directory, filename);
On Unix platforms, if the filename contains globbing patterns, such as [ab],
EnumerateFiles (and EnumerateDirectories) will perform the globbing. Using
globbing patterns, a file named 'file[txt].txt' is reported as not existing.
This fix changes the file-existence test on Unix to use a native function
instead of either of the Directory.EnumerateXXX functions.
* Fix for AppVeyor failure
* Changes per code review, and a couple of letter-casing changes.
2a739afa9c