Handle unexpected diagnostics that aren't in "detail message" format.

[netdpb]

Otherwise they were getting swallowed and never emitted even in details mode.

[cpovirk]

Handle unexpected diagnostics that aren't emitted by the framework as "detail messages".

I mis-parsed that at first: The diagnostics are emitted, but they're emitted in a format other than the detail-message format :) SGTM.

[netdpb]

Thanks. I've updated the title to be less misparseable.