[gnome-calculator] Fix Vala warning about default values

[Robert Ancell <rancell src gnome org>]

commit 4d1fdc589df3544961d4d89ab633b131cd05f3f1
Author: Robert Ancell <robert ancell canonical com>
Date:   Tue Oct 15 10:33:59 2013 +1300

    Fix Vala warning about default values

 src/equation.vala      |    2 +-
 src/math-equation.vala |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/equation.vala b/src/equation.vala
index 361f047..0669205 100644
--- a/src/equation.vala
+++ b/src/equation.vala
@@ -114,7 +114,7 @@ public class Equation
         this.expression = expression;
     }
 
-    public new Number? parse (out uint representation_base = null, out ErrorCode error_code = null, out 
string error_token = null, out uint error_start = null, out uint error_end = null)
+    public new Number? parse (out uint representation_base = null, out ErrorCode error_code = null, out 
string? error_token = null, out uint? error_start = null, out uint? error_end = null)
     {
         var parser = new EquationParser (this, expression);
         mp_clear_error ();
diff --git a/src/math-equation.vala b/src/math-equation.vala
index b97eae6..fb2051b 100644
--- a/src/math-equation.vala
+++ b/src/math-equation.vala
@@ -859,7 +859,7 @@ public class MathEquation : Gtk.TextBuffer
         }
     }
 
-    private Number? parse (string text, out uint representation_base, out ErrorCode error_code = null, out 
string error_token = null, out uint error_start, out uint error_end)
+    private Number? parse (string text, out uint representation_base, out ErrorCode error_code = null, out 
string? error_token = null, out uint? error_start = null, out uint error_end = null)
     {
         var equation = new MEquation (this, text);
         equation.base = serializer.get_base ();