Additional overload of Path.GetFullPath that takes the current folder

[HugoRoss]

Request:
I would like to see 4 more overloads of Path.GetFullPath (method signatures see below) that accept the current folder as an additional argument.

    public static string GetFullPath(string path, string currentFolder) { }
    public static string GetFullPath(string path, string currentFolder, GetFullPathOptions options) { }
    public static string GetFullPathTransacted(KernelTransaction transaction, string path, string currentFolder) { }
    public static string GetFullPathTransacted(KernelTransaction transaction, string path, string currentFolder, GetFullPathOptions options) { }

Reasons:

1. As mentioned in the method description, Path.GetFullPath is not thread-safe because it's accessing Environment.CurrentDirectory to determine the directory that may change between or during the call. If I can store the CurrentDirectory in a local variable and pass it to Path.GetFullPath I can call it n times in a row and get consistent results.
2. Environment.CurrentDirectory throws an exception, if the folder does not exist, disallowing it to get the full path of a not yet existing current folder. Imagine a setup scenario where the target folder only exists yet as a string result coming from a wizard page (the root folder where the application is going to be installed).

[HugoRoss]

This request is outdated if #304 is taken into account. My new suggestion is to replace the string currentFolder by a CurrentFolderCache currentFolders parameter with a class definition that could look something like this:

public class CurrentFolderCache {

	private String _CurrentFolder;
	private ConcurrentDictionary<Char, String> _CurrentFolderPerDrive;

	public CurrentFolderCache() {
		_CurrentFolderPerDrive = new ConcurrentDictionary<Char, String>();
	}

	/// <summary>Gets or sets the current folder used for a Path.GetFullPath(..) operations. This is done
	/// without affecting the processes current folder (Environment.CurrentDirectory). If the getter is
	/// called and the internal value is null, the value from Environment.CurrentDirectory if fetched
	/// and assigned to the internal variable for successive calls.</summary>
	public String CurrentFolder {
		get {
			String myResult = _CurrentFolder;
			if (myResult == null) {
				myResult = Environment.CurrentDirectory;
				_CurrentFolder = myResult;
			}
			return myResult;
		}
		set {
			if (value != null) CheckWhetherWellFormedAbsolutePath(value);
			_CurrentFolder = value;
		}
	}

	/// <summary>Gets or sets the current folder per drive letter used for Path.GetFullPath(..) operations. 
	/// This is done without affecting the current folder per drive letter (stored in special environment 
	/// variables). If the getter is called and the internal value for the given drive letter is null, the 
	/// value from the according environment variable if fetched and assigned to the internal cache for 
	/// successive calls.</summary>
	public String this[String driveLetter] {
		get {
			//Check arg
			CheckDriveLetter(driveLetter);
			//Get from cache
			Char myKey = driveLetter[0];
			String myResult = null;
			if (_CurrentFolderPerDrive.TryGetValue(myKey, out myResult)) {
				return myResult;
			}
			//Add to cache and return
			myResult = GetCurrentFolderPerDrive(driveLetter);
			myResult = _CurrentFolderPerDrive.GetOrAdd(myKey, myResult);
			return myResult;
		}
		set {
			//Check args
			CheckDriveLetter(driveLetter);
			if (value != null) CheckWhetherWellFormedAbsolutePath(value);
			//Update cache
			Char myKey = driveLetter[0];
			_CurrentFolderPerDrive.AddOrUpdate(myKey, value, (k, o) => value);
		}
	}

	private void CheckDriveLetter(String driveLetter) {
		if ((driveLetter == null) || (driveLetter.Length == 0) || (driveLetter.Length > 2)) {
			throw new ArgumentException(@"A drive letter expected, e.g. ""C:"" or ""C""!", nameof(driveLetter));
		}
	}

	private void CheckWhetherWellFormedAbsolutePath(String folder) {
		//TODO: Implement
	}

	private String GetCurrentFolderPerDrive(String driveLetter) {
		//TODO: Implement. See #304
		throw new NotImplementedException();
	}

}