Removing orphan check/flag files.
Limit bad advice given for erroneous pattern.

Don't suggest "_: <none>" as an alternative when the pattern
type doesn't conform to the expected type.
Restore --show-diff to partest-ack.

Looks like that issue was operator error. However partest
option --show-log really has gone missing.
Merge pull request #2930 from retronym/topic/patmat-inference-prep

Topic/patmat inference prep