Fix security-enabled delete handling for nonexistent resources.
Refactor forbidden/2 and resource validation helper functions.
Further refactorings to forbidden/2.

- Move method_to_term to riak_kv_wm_utils.
- Put resulting and unexplained dialyzer error into ignore file.
- Rename validate_unforbidden.
Fix R15 dialyzer issue in riak_kv_wm_utils.

- Remove the case clause after the http_uri:parse/1, it has been
deprecated.
- Remove the entry for the dialyzer warning in the ignore file.
Fix whitespace.
Merge pull request #952 from basho/bugfix/jra/issues_917_918

Fix security-enabled delete handling for nonexistent resources.

Reviewed-by: kellymclaughlin