small findSigns.py fix -- loading regions with north_direction pre-rotates

What we want in findSigns.py is the raw map data.

contrib/findSigns.py

@@ -69,7 +69,7 @@ for dirpath, dirnames, filenames in os.walk(worlddir):
         if matcher.match(f):
             print f
             full = os.path.join(dirpath, f)
-            r = nbt.load_region(full,north_direction)
+            r = nbt.load_region(full)
             chunks = r.get_chunks()
             for x,y in chunks:
                 chunk = r.load_chunk(x,y).read_all()                

overviewer_core/nbt.py

@@ -200,7 +200,7 @@ class MCRFileReader(object):
     chunks (as instances of NBTFileReader), getting chunk timestamps,
     and for listing chunks contained in the file."""
     
-    def __init__(self, filename, north_direction):
+    def __init__(self, filename, north_direction='lower-left'):
         self._file = None
         self._filename = filename
         self.north_direction = north_direction