Apply 2to3 has_key fixer to Bio.trie

I appear to have wrongly been under the impression that
the C code in Bio/triemodule.c would need updating too.

$ 2to3 --no-diffs -n -w -f has_key Bio BioSQL Tests Doc Scripts
RefactoringTool: Refactored Bio/triefind.py
RefactoringTool: Refactored Tests/test_trie.py
RefactoringTool: Files that were modified:
RefactoringTool: Bio/triefind.py
RefactoringTool: Tests/test_trie.py
No longer need the 2to3 has_key fixer
Use assertTrue and assertFalse in test_trie.py