[LyX/master] Clarify member variable documentation

[Georg Baum]

commit 9d8839f6884d3ef15cf5047815689c8b56c166ee
Author: Georg Baum <b...@lyx.org>
Date:   Sun Nov 16 19:15:13 2014 +0100

    Clarify member variable documentation

diff --git a/src/OutputParams.h b/src/OutputParams.h
index 598b575..87d8fcd 100644
--- a/src/OutputParams.h
+++ b/src/OutputParams.h
@@ -116,6 +116,8 @@ public:
        mutable std::string document_language;
 
        /** The master language. Non-null only for child documents.
+           Note that this is not the language of the top level master, but
+           of the direct parent for nested includes.
         */
        mutable Language const * master_language;