Make the missing class warning opt-out

src/BufferParams.cpp

@@ -632,7 +632,7 @@ string BufferParams::readToken(Lexer & lex, string const & token,
 						 "See section 3.1.2.2 (Class Availability) of the\n"
 						 "User's Guide for more information."), desc, prereqs);
 			frontend::Alert::warning(_("Document class not available"),
-				       msg);
+				       msg, true);
 		}
 	} else if (token == "\\begin_preamble") {
 		readPreamble(lex);

status.21x

@@ -48,6 +48,9 @@ What's new
 - Fix the profile script used on cygwin to comply with the latest cygwin/X
   X server which, by default, does not anymore listen to tcp connections.
 
+- Add a "Do not show again" checkbox to the warning that is issued when the
+  LaTeX class/packages are missing for a given layout (bug 9420).
+
 
 * DOCUMENTATION AND LOCALIZATION