Use a dedicated field for cached search timestamps

Fix a cache corruption issue by using a new "cached" field to hold
the timestamp for cached correlation search results. Previously the
"description" field was being overloaded, but this could cause the
cache to no longer load because of duplicate fields.

weather.py

@@ -1134,7 +1134,7 @@ def guess(
         )
         search_cache = ["\n"]
         search_cache.append( "[%s]\n" % search[0] ) 
-        search_cache.append( "description = cached %s\n" % nowstamp )
+        search_cache.append( "cached = %s\n" % nowstamp )
         for uriname in sorted(uris.keys()):
             search_cache.append( "%s = %s\n" % ( uriname, uris[uriname] ) )
         real_cachedir = os.path.expanduser(cachedir)