Convert calibre modules to ebook_converter.

Here is the first batch of modules, which are needed for converting
several formats to LRF. Some of the logic has been change, more cleanups
will follow.

ebook_converter/ebooks/pdb/header.py

@@ -13,7 +13,7 @@ __docformat__ = 'restructuredtext en'
 import re
 import struct
 import time
-from polyglot.builtins import long_type
+from ebook_converter.polyglot.builtins import long_type
 
 
 class PdbHeaderReader(object):