changed --sep_vn to be not default

meloptions.h

@@ -196,8 +196,8 @@ class MelodicOptions {
    joined_whiten(string("--sep_whiten"), false,
 	   string("switch on separate whitening"), 
 	   false, no_argument, false),
-   joined_vn(string("--sep_vn"), false,
-   	   string("switch on group variance nomalisation (as opposed to separate VN)"), 
+   joined_vn(string("--sep_vn"), true,
+   	   string("switch on separate variance nomalisation (as opposed to separate VN)"), 
        false, no_argument),
    dr_pca(string("--mod_pca"), true,
 	   string("switch off modified PCA for concat ICA"),