Before this patch, the result code was a mixture of `int` and
`CURLcode`.
Also adjust casts and fix a couple of minor issues found along the way.
Cherry-picked from #13489Closes#13600
- they are mostly pointless in all major jurisdictions
- many big corporations and projects already don't use them
- saves us from pointless churn
- git keeps history for us
- the year range is kept in COPYING
checksrc is updated to allow non-year using copyright statements
Closes#10205
The 550 is overused as a return code for multiple error case, e.g.
file not found and/or insufficient permissions to access the file.
So we cannot fail hard in this case.
Adjust test 511 since we now fail later.
Add new test 3027 which check that when MDTM failed, but the file could
actually be retrieved, that in this case no filetime is provided.
Reported-by: Michael Heimpold
Fixes#9357Closes#9387