multiple update to cdi

Multiple features are added to the cdi.py module: described in the "UPDATE" file inside the folder. Some of them are listed 
(*) Re-download PDF files using "wget" if they are not found from Heritrix mirror directory.
(*) Throw the _mysql_exceptions.Warnings exception when a URL is not able to be saved into the "url" field of database.
(*) Add a urlfilters.py module and add "urllengthrule" and "blacklistrule".