Open database with correct encoding in mmap and mem cache mode

This is already done when database is open without caching or mmap. The current implementation
leads to different behaviour when different flags are used.

pygeoip/__init__.py

@@ -101,13 +101,13 @@ class GeoIP(object):
             self._flags &= ~const.MMAP_CACHE
 
         if self._flags & const.MMAP_CACHE:
-            f = open(filename, 'rb')
+            f = codecs.open(filename, 'rb', ENCODING)
             access = mmap.ACCESS_READ
             self._filehandle = mmap.mmap(f.fileno(), 0, access=access)
             f.close()
 
         elif self._flags & const.MEMORY_CACHE:
-            f = open(filename, 'rb')
+            f = codecs.open(filename, 'rb', ENCODING)
             self._memoryBuffer = f.read()
             iohandle = BytesIO if PY3 else StringIO
             self._filehandle = iohandle(self._memoryBuffer)