fs: warn the user when using a remote name without a colon

A very common mistake for new users of rclone is to use a remote name
without a colon. This can be on the command line or in the config when
setting up a crypt backend.

This change checks to see if the user uses a path which matches a
remote name and gives an NOTICE like this if they do

    NOTICE: "remote" refers to a local folder, use "remote:" to refer to your remote or "./remote" to hide this warning

See: https://forum.rclone.org/t/sync-to-onedrive-personal-lands-file-in-localfilesystem-but-not-in-onedrive/32956

fs/config.go

@@ -29,6 +29,12 @@ var (
 		return errors.New("no config file set handler")
 	}
 
+	// Check if the config file has the named section
+	//
+	// This is a function pointer to decouple the config
+	// implementation from the fs
+	ConfigFileHasSection = func(section string) bool { return false }
+
 	// CountError counts an error.  If any errors have been
 	// counted then rclone will exit with a non zero error code.
 	//