Adjust ipcache to observe new region

THIS WILL INVALIDATE THE EXISTING CACHE!
The new cache now pulls data from all three of geoip, ip2location, and
ipinfo, and stores it in the relatively simple city;region;country
format.

The old format would either store city;country or store
countrycode;country;region;city directly from ip2location, so it is much
more consistent with this change.

lib/location.py

@@ -103,22 +103,22 @@ def ipcachewrite(ip_addr, location):
         # like ip2location format, but reversed
 
 def ipcache(ip_addr):
-    cached = os.path.join(IP2LCACHE, ip_addr)
+    """ Retrieve a location from cache by ip addr
+        Returns a triple of (CITY, REGION, COUNTRY) or None
+    """
+    cachefile = os.path.join(IP2LCACHE, ip_addr)
     if not os.path.exists(IP2LCACHE):
         os.makedirs(IP2LCACHE)
 
-    location = None
-
-    if os.path.exists(cached):
-        location = open(cached, 'r').read().split(';')
-        if len(location) > 3:
-            return location[3], location[1]
-        elif len(location) > 1:
-            return location[0], location[1]
-        else:
-            return location[0], None
+    if os.path.exists(cachefile):
+        try:
+            city, region, country = open(cachefile, 'r').read().split(';')
+            return city, region, country
+        except ValueError:
+            # cache entry is malformed: should be city;region;country
+            return None
+    return None
 
-    return None, None
 
 def ip2location(ip_addr):
     """Convert IP address `ip_addr` to a location name"""