Use correct Image module import

Otherwise Tribler doesn't start (Ubuntu 14.04)
Merge pull request #961 from gjedeer/patch-1

Use correct Image module import
make TFTP stop working after shutdown
fix improper error messages to warning
fix PIL Image import
Merge pull request #962 from LipuFei/fixes

Some fixes
Less logging when circuit is destroyed
Fix for ignore_candidates
Merge pull request #965 from Tribler/fix_ignore_candidates

Fix for ignore_candidates
Merge pull request #963 from egbertbouman/less_logging

Less logging when circuit is destroyed