logfile diversion

[Richard Durbin]

Following Suzanna's letter, and a brief exchange with Jean, I have changed
messubs.c so that if messdump() can not open the requested logfile then it
writes to stderr, starting with a message of complaint about failing to
open the file.  Here is the diff to my previous version of messubs.c:

164,169c164,166
<         { dumpfil = stderr ;
<           fprintf (stderr, "\n** Can't open log file %s - using stderr **\n",
<                    messdumpfilename) ;
<         }
<       else
<         fprintf (dumpfil,"\n%s %s\n", timeStamp(), dateStamp()) ;
---
>         messcrash ("Can't open dump file %s", messdumpfilename) ;
>
>       fprintf (dumpfil,"\n%s %s\n", timeStamp(), dateStamp()) ;

Richard