fixed issue 1850, caching errors when unable to obtain plugin list

VERSION

@@ -1 +1 @@
-Version 2.8.2-stable+timestamp.2014.01.09.11.46.01
+Version 2.8.2-stable+timestamp.2014.01.11.15.02.21

applications/admin/controllers/default.py

@@ -1907,10 +1907,14 @@ def plugins():
     app = request.args(0)
     from serializers import loads_json
     if not session.plugins:
-        rawlist = urllib.urlopen("http://www.web2pyslices.com/" +
-            "public/api.json/action/list/content/Package?package" +
-            "_type=plugin&search_index=false").read()
-        session.plugins = loads_json(rawlist)
+        try:
+            rawlist = urllib.urlopen("http://www.web2pyslices.com/" +
+                                     "public/api.json/action/list/content/Package?package" +
+                                     "_type=plugin&search_index=false").read()
+            session.plugins = loads_json(rawlist)
+        except:
+            response.flash = T('Unable to download the list of plugins')
+            session.plugins = []
     return dict(plugins=session.plugins["results"], app=request.args(0))
 
 def install_plugin():