Fixed default value for inline widgets

gui/modules/constant_configuration.py:
 - ConstantWidgetBase:
   Show default value if strVal is empty
   strValue was always set before, which worked in QLineEdit but broke inline widgets

vistrails/gui/modules/constant_configuration.py

@@ -91,9 +91,10 @@ def __init__(self, param):
         ConstantWidgetMixin.__init__(self, value)
 
         self.psi = psi
-        if psi and psi.default:
+        if psi and psi.default and param.strValue == '':
             self.setDefault(psi.default)
-        self.setContents(param.strValue)
+        else:
+            self.setContents(param.strValue)
 
     def setDefault(self, value):
         # default to setting the contents silenty