[patch] fix bug 5610: description wrong in beamer

[Jürgen Spitzmüller]

http://bugzilla.lyx.org/show_bug.cgi?id=5610

Objections? If not, I'd like to put this into 1.6.1svn (and trunk), since it 
strikes my straightforward.

Jürgen
Index: src/Paragraph.cpp
===================================================================
--- src/Paragraph.cpp	(Revision 27825)
+++ src/Paragraph.cpp	(Arbeitskopie)
@@ -921,7 +921,9 @@
 		column += 17;
 		break;
 
-	case '*': case '[':
+	case '*':
+	case '[':
+	case ']':
 		// avoid being mistaken for optional arguments
 		os << '{';
 		os.put(c);