Changed a few fields to be optional.

Found a fairly difficult bug involved with Field instances
being shared across Records. The issue is that Field instances
are static. I either need to implement a way to instantiate
copies of all the Fields per-record, or write a wrapping
interface which provides a unique value store on a per-Record
basis.

pyaccuwage/fields.py

@@ -12,6 +12,7 @@ class ValidationError(Exception):
             return "(%s.%s) %s" % (self.field.parent_name, self.field.name, self.msg)
         else:
             return repr(self.msg)
+ 
 
 class Field(object):
     creation_counter = 0
@@ -49,6 +50,12 @@ class Field(object):
         self.value = s.strip()
 
 
+class FieldInterface(object):
+    def __init__(self, value_dict, field):
+        self.value_dict = value_dict
+        self.field = field
+
+
 class TextField(Field):    
     def validate(self):
         if self.value == None and self.required: