Shift wiki and course.xml caching to use newly defined 'general' cache, separate from sessions left in 'default'

--HG--
branch : cache_separation

courseware/content_parser.py

@@ -11,10 +11,11 @@ from lxml import etree
 
 try: # This lets us do __name__ == ='__main__'
     from django.conf import settings
-    from django.core.cache import cache
+
     from student.models import UserProfile
     from student.models import UserTestGroup
     from mitxmako.shortcuts import render_to_response, render_to_string
+    from util.cache import cache
 except: 
     settings = None 
 

simplewiki/models.py

@@ -3,7 +3,6 @@ import os
 
 from django import forms
 from django.contrib.auth.models import User
-from django.core.cache import cache
 from django.core.urlresolvers import reverse
 from django.db import models
 from django.db.models import signals
@@ -11,6 +10,8 @@ from django.utils.translation import ugettext_lazy as _
 from markdown import markdown
 
 from settings import *
+from util.cache import cache
+
 
 class ShouldHaveExactlyOneRootSlug(Exception):
     pass

util/cache.py

@@ -0,0 +1,16 @@
+"""
+This module aims to give a little more fine-tuned control of caching and cache
+invalidation. Import these instead of django.core.cache.
+
+Note that 'default' is being preserved for user session caching, which we're 
+not migrating so as not to inconvenience users by logging them all out.
+"""
+from django.core import cache
+
+# If we can't find a 'general' CACHE defined in settings.py, we simply fall back
+# to returning the default cache. This will happen with dev machines.
+try:
+    cache = cache.get_cache('general')
+except ValueError:
+    cache = cache.cache
+