Executing the script 'tst' (included in the patch)
on a window clears its contents, but the change
can't be undone.  This patch fixes it.

Also, I think xfid.c:218 should be removed because
xfid.c:224 takes care of resetting 'nomark' after
all open Xfids of data file are closed, but I
haven't tested it — hence not included in this
patch.

Notes:
Fri Apr 6 10:02:04 EDT 2007 rsc
    Since acme is already inserting marks for each text replacement,
    I don't believe that making opening data make a mark is correct.
    For example, if I cat /mnt/acme/$id/data, that shouldn't mark 
    anything.
    


Reference: /n/sources/patch/sorry/acme4-data-undo
Date: Sun Nov 12 13:36:48 CET 2006
Signed-off-by: arvindht@gmail.com
Reviewed-by: rsc

--- /sys/src/cmd/acme/xfid.c	Sun Nov 12 05:52:41 2006
+++ /sys/src/cmd/acme/xfid.c	Sun Nov 12 05:52:38 2006
@@ -110,6 +110,8 @@
 			break;
 		case QWdata:
 		case QWxdata:
+			seq++;
+			filemark(t->file);
 			w->nopen[q]++;
 			break;
 		case QWevent: