Bump tools.mk.
Ignore additional dialyzer files.
Ensure stat can be registered.

Resolves:

riak_kv_stat.erl:489: Expression produces a value of type 'ok' | {'error',_,'metric_already_exists' | 'unsupported_metric_type'}, but this value is unmatched
Ignore tags file.
Ignore the result of the list comprehension.

Resolves:

riak_kv_stat.erl:325: Expression produces a value of type [any()], but this value is unmatched
Normalize return value of function.

Resolves:

riak_kv_stat.erl:577: Expression produces a value of type 'ok' | ['ok' | {'error',_,'metric_already_exists' | 'nonexistent_metric' | 'unsupported_metric_type'}], but this value is unmatched
Assert we can create the metric.

Resolves:

riak_kv_stat.erl:324: Expression produces a value of type 'ok' | {'error',_,'metric_already_exists' | 'unsupported_metric_type'}, but this value is unmatched
Ignore the result of the list comprehension.

Resolves:

riak_kv_stat.erl:310: Expression produces a value of type [any()], but this value is unmatched
Remove incorrect type specification.