Handle bogus dates better.
 [rsc] --rw-rw-r-- M 197601 glenda sys 5684 Nov  2 10:37 sys/src/cmd/ip/imap4d/date.c
	/n/sourcesdump/2005/1102/plan9/sys/src/cmd/ip/imap4d/date.c:30,36 - 
	/n/sourcesdump/2005/1103/plan9/sys/src/cmd/ip/imap4d/date.c:30,36
	  	if(tm->tzoff < 0)
	  		plus = "";
	  	m = 0;
	- 	if(tm->wday != 8){
	+ 	if(0 <= tm->wday && tm->wday < 7){
	  		m = snprint(s, n, "%s, ", wdayname[tm->wday]);
	  		if(m < 0)
	  			return m;