Fix display of MH-history if parameter names do not have same length

In this case, cell2mat fails, because the dimensions are not consistent. Using char() instead padds with spaces

(cherry picked from commit 47b1a2df)

matlab/internals.m

@@ -137,7 +137,7 @@ if strcmpi(flag,'--load-mh-history') || strcmpi(flag,'--display-mh-history')
             d1s = size(d1,2);
             d2s = size(d2,2);
             c0 = repmat('   ',length(names)+2,1);
-            c1 = char(' ', repmat('+',1,size(cell2mat(names),2)), cell2mat(names));
+            c1 = char(' ', repmat('+',1,size(char(names),2)), char(names));
             s1 = char(' || ','++++',repmat(' || ', length(names),1));
             t1 = repmat(' ',1,d1s);
             if d1s<=7