Fix cut-and-paste errors in nonfatal() implementations.

Fix cut-and-paste errors in nonfatal() implementations.

Unix GUI programs should not say 'Fatal Error' in the message box
title, and Plink should not destroy its logging context as a side
effect of printing a non-fatal error. Both appear to have been due to
inattentive cut and paste from the pre-existing fatal error functions.

git-svn-id: http://svn.tartarus.org/sgt/putty@10044 cda61777-01e9-0310-a592-d414129be87e