kingst-la2016: rephrase diagnostics to improve user perception

kingst-la2016: rephrase diagnostics to improve user perception

Rephrase diagnostics messages so that users easier can digest them. Keep
implementation details out of messages which are seen by default, stick
those into developer centric messages that correspond to higher verbosity
levels. Consistently start with capital letters and end in punctuation.
Drop exclamation marks. Use all caps for acronyms. Don't break format
strings so that developers can search for messages reported by users.
Break a few long source code text lines (but not all of them).