Fixes CDB_UserDataSize failing due ERROR: relation "*" does not exist.

Adds new _CDB_total_relation_size function that handles nonexistent
tables and does fallback to size=0.

That function could be used to cache total relation size or query another
table view with a cached total relation size.

Fixes #108

Makefile

@@ -1,7 +1,7 @@
 # cartodb/Makefile
 
 EXTENSION = cartodb
-EXTVERSION = 0.8.2
+EXTVERSION = 0.8.3
 
 SED = sed
 
@@ -41,6 +41,7 @@ UPGRADABLE = \
   0.7.4 \
   0.8.0 \
   0.8.1 \
+  0.8.2 \
   $(EXTVERSION)dev \
   $(EXTVERSION)next \
   $(END)
@@ -120,5 +121,5 @@ test_extension_new:
 
 legacy_tests: legacy_regress 
 
-installcheck: legacy_tests test_extension_new test_organization
+installcheck: legacy_tests