windows: Stop drive letters (eg C:) getting mixed up with remotes (eg drive:)

This was done by stopping the user configuring single letter remotes
and making sure we don't treat single letter remotes as a remote name,
but as a drive letter.

fs/config.go

@@ -330,9 +330,19 @@ func EditConfig() {
 			name := ChooseRemote()
 			EditRemote(name)
 		case 'n':
-			fmt.Printf("name> ")
-			name := ReadLine()
-			NewRemote(name)
+			for {
+				fmt.Printf("name> ")
+				name := ReadLine()
+				switch {
+				case name == "":
+					fmt.Printf("Can't use empty name\n")
+				case isDriveLetter(name):
+					fmt.Printf("Can't use %q as it can be confused a drive letter\n", name)
+				default:
+					NewRemote(name)
+					break
+				}
+			}
 		case 'd':
 			name := ChooseRemote()
 			DeleteRemote(name)

fs/driveletter.go

@@ -0,0 +1,12 @@
+// +build !windows
+
+package fs
+
+// isDriveLetter returns a bool indicating whether name is a valid
+// Windows drive letter
+//
+// On non windows platforms we don't have drive letters so we always
+// return false
+func isDriveLetter(name string) bool {
+	return false
+}

fs/driveletter_windows.go

@@ -0,0 +1,13 @@
+// +build windows
+
+package fs
+
+// isDriveLetter returns a bool indicating whether name is a valid
+// Windows drive letter
+func isDriveLetter(name string) bool {
+	if len(name) != 1 {
+		return false
+	}
+	c := name[0]
+	return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
+}

fs/fs.go

@@ -196,9 +196,6 @@ type Dir struct {
 // A channel of Dir objects
 type DirChan chan *Dir
 
-// Pattern to match a url
-var matcher = regexp.MustCompile(`^([\w_-]+):(.*)$`)
-
 // Finds a FsInfo object for the name passed in
 //
 // Services are looked up in the config file
@@ -211,16 +208,22 @@ func Find(name string) (*FsInfo, error) {
 	return nil, fmt.Errorf("Didn't find filing system for %q", name)
 }
 
+// Pattern to match an rclone url
+var matcher = regexp.MustCompile(`^([\w_-]+):(.*)$`)
+
 // NewFs makes a new Fs object from the path
 //
 // The path is of the form remote:path
 //
 // Remotes are looked up in the config file.  If the remote isn't
 // found then NotFoundInConfigFile will be returned.
+//
+// On Windows avoid single character remote names as they can be mixed
+// up with drive letters.
 func NewFs(path string) (Fs, error) {
 	parts := matcher.FindStringSubmatch(path)
 	fsName, configName, fsPath := "local", "local", path
-	if parts != nil {
+	if parts != nil && !isDriveLetter(parts[1]) {
 		configName, fsPath = parts[1], parts[2]
 		var err error
 		fsName, err = ConfigFile.GetValue(configName, "type")