When the COPY_FILE operation fails optionally capture the error message
with a COPY_FILE_ERROR option instead of reporting the error
immediately. This gives callers a chance to do something else or report
the error.
Teach the RunCMake.try_compile test to cover bad argument combinations
involving COPY_FILE_ERROR. Teach the TryCompile test to cover the case
of a COPY_FILE error message captured by COPY_FILE_ERROR.
Brad King