ClientRead: "close" flushes the output buffer

Add a new CommandResult code called "FINISH" which, unlike "CLOSE",
will attempt to flush the output buffer.  This is a one-shot attempt;
it will do one write, and not try again.

NEWS

@@ -1,4 +1,6 @@
 ver 0.18.2 (2013/??/??)
+* protocol:
+  - "close" flushes the output buffer
 * input:
   - curl: fix bug with redirected streams
 * playlist:

src/ClientRead.cxx

@@ -57,6 +57,11 @@ Client::OnSocketInput(void *data, size_t length)
 		main_loop->Break();
 		return InputResult::CLOSED;
 
+	case CommandResult::FINISH:
+		if (Flush())
+			Close();
+		return InputResult::CLOSED;
+
 	case CommandResult::CLOSE:
 		Close();
 		return InputResult::CLOSED;

src/command/CommandResult.hxx

@@ -47,6 +47,12 @@ enum class CommandResult {
 	 */
 	ERROR,
 
+	/**
+	 * The client has asked MPD to close the connection.  MPD will
+	 * flush the remaining output buffer first.
+	 */
+	FINISH,
+
 	/**
 	 * The connection to this client shall be closed.
 	 */

src/command/OtherCommands.cxx

@@ -99,7 +99,7 @@ CommandResult
 handle_close(gcc_unused Client &client,
 	     gcc_unused int argc, gcc_unused char *argv[])
 {
-	return CommandResult::CLOSE;
+	return CommandResult::FINISH;
 }
 
 CommandResult