[LyX/master] Const.

[Richard Heck]

commit f7fdf49f646f396ffd6d04fd9124f0b933f19501
Author: Richard Heck <rgh...@lyx.org>
Date:   Mon Mar 28 12:39:55 2016 -0400

    Const.

diff --git a/src/TextClass.cpp b/src/TextClass.cpp
index e71fed0..c9655df 100644
--- a/src/TextClass.cpp
+++ b/src/TextClass.cpp
@@ -1511,7 +1511,7 @@ InsetLayout const & DocumentClass::insetLayout(docstring 
const & name) const
 
 
 InsetLayout const & DocumentClass::plainInsetLayout() {
-       static InsetLayout plain_insetlayout_;
+       static const InsetLayout plain_insetlayout_;
        return plain_insetlayout_;
 }