Fix migration issues:

- MySQL 5.5 doesn't support the now() call as a default
  - Postgres migration isn't auto-committed, so we have to check if the table exists first

util/uncompressedsize.py

@@ -3,7 +3,7 @@ import zlib
 import sys
 
 from data import model
-from data.database import ImageStorage
+from data.database import ImageStorage, configure
 from app import app, storage as store
 from data.database import db, db_random_func
 from util.gzipstream import ZLIB_GZIP_WINDOW
@@ -14,11 +14,13 @@ logger = logging.getLogger(__name__)
 
 CHUNK_SIZE = 5 * 1024 * 1024
 
-
 def backfill_sizes_from_data():
   logger.setLevel(logging.DEBUG)
   logger.debug('Starting uncompressed image size backfill')
-  
+
+  # Make sure we have a reference to the current DB.
+  configure(app.config)
+
   formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
   
   ch = logging.StreamHandler(sys.stdout)
@@ -27,6 +29,14 @@ def backfill_sizes_from_data():
 
   encountered = set()
 
+  # Try reading the ImageStorage table count. If it doesn't exist, then this is a postgres
+  # initial setup migration and we can skip this step anyway.
+  try:
+    ImageStorage.select().count()
+  except:
+    logger.debug('Skipping migration for new setup')
+    return
+
   while True:
     # Load the record from the DB.
     batch_ids = list(ImageStorage