Add BMessageFormat class.

This can be used to format complex messages properly. It moves the
complexity of handling plural forms, gender, and anything else needed
into the localizable string, rather than hardcoding it in the code.

This moves the difficulty of handling these things properly to people
doing translations, rather than relying on developers to do it.

Fixes #10755, but our localization must now be updated to make use of
the feature.

headers/os/locale/MessageFormat.h

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2014, Haiku, Inc.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _B_MESSAGE_FORMAT_H_
+#define _B_MESSAGE_FORMAT_H_
+
+
+#include <Format.h>
+
+
+class BMessageFormat: public BFormat {
+public:
+			status_t			Format(BString& buffer, const BString message,
+									const int32 arg);
+};
+
+
+#endif