* Create new help page for comment template context variables

( see /help/context/; also linked from comment form)
* Refactor API help page to share template with context help
* Allow a limited number of Ticket & Queue model fields to be 
  accessible in comments, as per 'Help' page.
* New function in lib.py to build a dict of 'safe' fields from 
  ticket & queue, to prevent the power of the Django model API 
  from exposing things like passwords (imagine if a user typed
  a comment containing {{ ticket.queue.email_box_password }} !!!!
* When accessing the ticket list with no filter params (eg by 
  clicking on the "Tickets" button in the menu), the default 
  search is for tickets that aren't closed, rather than showing
  all tickets.
* Updated English locale with changed message strings.

urls.py

@@ -91,11 +91,6 @@ urlpatterns += patterns('',
         'helpdesk.views.api.api',
         name='helpdesk_api'),
 
-    url(r'^api/$',
-        'django.views.generic.simple.direct_to_template',
-        {'template': 'helpdesk/api_help.html',},
-        name='helpdesk_api_help'),
-
     url(r'^login/$',
         'django.contrib.auth.views.login',
         name='login'),
@@ -118,3 +113,15 @@ urlpatterns += patterns('helpdesk.views.kb',
     url(r'^kb/(?P<item>[0-9]+)/vote/$',
         'vote', name='helpdesk_kb_vote'),
 )
+
+urlpatterns += patterns('',
+    url(r'^api/$',
+        'django.views.generic.simple.direct_to_template',
+        {'template': 'helpdesk/help_api.html',},
+        name='helpdesk_api_help'),
+    
+    url(r'^help/context/$',
+        'django.views.generic.simple.direct_to_template',
+        {'template': 'helpdesk/help_context.html',},
+        name='helpdesk_help_context'),
+)