scp: Have `fatal()' append a newline to the message

Date: Wed, 4 Nov 2015 20:33:19 -0000
It would seem that it's standard practice not to include a newline in the message
text, but that results in poor formatting, as a shell's command line then begins
on the line of the error message itself.

This commit simply instructs `fatal()' to append a newline after the message,
which should be suitable behavior for all of the invocations I've come across.