[#42] Dump non-string extras with json

Convert any non-string extra values to strings using json.dumps(),
instead of just deleting them.

ckanext/harvest/harvesters/ckanharvester.py

@@ -254,10 +254,16 @@ class CKANHarvester(HarvesterBase):
                     package_dict['groups'] = []
                 package_dict['groups'].extend([g for g in default_groups if g not in package_dict['groups']])
 
-            # Delete any extras whose values are not strings, as these cause
-            # errors from CKAN when trying to create/update the package.
+            # Find any extras whose values are not strings and try to convert
+            # them to strings, as non-string extras are not allowed anymore in
+            # CKAN 2.0.
             for key in package_dict['extras'].keys():
                 if not isinstance(package_dict['extras'][key], basestring):
+                    try:
+                        package_dict['extras'][key] = json.dumps(
+                                package_dict['extras'][key])
+                    except TypeError:
+                        # If converting to a string fails, just delete it.
                         del package_dict['extras'][key]
 
             # Set default extras if needed