registration: add support for year of birth

this is only in dav_registration for now. dav_events is following.

dav_registration/forms.py

@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+import datetime
 import logging
 from django import forms
 from django.utils.translation import ugettext, ugettext_lazy as _
@@ -25,6 +26,28 @@ class RegistrationForm(forms.ModelForm):
             'note': forms.Textarea(attrs={'rows': 5}),
         }
 
+    def clean_year_of_birth(self):
+        now = datetime.datetime.now()
+        year_now = now.year
+        max_age = 100
+        val = self.cleaned_data.get('year_of_birth')
+        if val > year_now:
+            raise forms.ValidationError(
+                ugettext(u'Dein Geburtsjahr liegt in der Zukunft?'
+                         u' Das finden wir gut,'
+                         u' aber bitte melde dich besser mal per E-Mail bei uns.'),
+                code='to_young',
+            )
+        elif val < (year_now - max_age):
+            raise forms.ValidationError(
+                ugettext(u'Du bist schon über %(max_age)d Jahre alt?'
+                         u' Das finden wir gut,'
+                         u' aber bitte melde dich besser mal per E-Mail bei uns.'),
+                params={'max_age': max_age},
+                code='to_old',
+            )
+        return val
+
     def clean_experience(self):
         val = self.cleaned_data.get('experience')
         if val == '':