Space out test_prepend_super_in_alias assert

Also tried to fix it, however the problem lies with how aliased methods
are done and their internal structure.

mruby simply aliases methods by grabbing the RProc and giving it a new name,
super then determines the original method to call by using the name

so a method called m, aliased as m2, will call the m2 super method instead of m

test/t/module.rb

@@ -720,17 +720,25 @@ assert('Module#prepend') do
     p = labeled_module("P") do
       def m; "P"+super; end
     end
+
     a = labeled_class("A") do
       def m; "A"; end
     end
+
     b = labeled_class("B", a) do
       def m; "B"+super; end
       alias m2 m
       prepend p
       alias m3 m
     end
-    assert_equal("BA", b.new.m2, bug7842)
-    assert_equal("PBA", b.new.m3, bug7842)
+
+    assert_nothing_raised do
+      assert_equal("BA", b.new.m2, bug7842)
+    end
+
+    assert_nothing_raised do
+      assert_equal("PBA", b.new.m3, bug7842)
+    end
   end
 
   assert 'test_prepend_each_classes' do