Allow a -D'date' option to be included with a -r'branch'

on a checkout.
this allows us to do:
cd /usr/src/sys
cvs update -rRELENGE_2_2 -D"Yesterday"
which has been a feature sorely needed for any project with active branches.

warning: this breaks on usr.sbin/pkg_install for some reason.
everything else works as advertised.
(other things allready break on pkg_install, so it's not the fault of
this patch, it just falls faul of another bug somewhere)
If I had more time I'd make -r always accept the same syntax as -j (tag:data)

contrib/cvs/src/rcs.c

@@ -1857,9 +1857,9 @@ RCS_getdatebranch (rcs, date, branch)
     free (xbranch);
     if (p == vers->branches->list)
     {
-	/* FIXME: This case would seem to imply that the RCS file is
-           somehow invalid.  Should we give an error message?  */
-	return (NULL);
+	   /* This happens when you have a couple of branches off a revision,
+	   and your branch has not diverged, but another has. */
+	return (xstrdup (cur_rev));
     }
 
     p = findnode (rcs->versions, p->key);

contrib/cvs/src/update.c

@@ -491,7 +491,7 @@ update_fileproc (callerdat, finfo)
 	&& tag != NULL
 	&& finfo->rcs != NULL)
     {
-	char *rev = RCS_getversion (finfo->rcs, tag, NULL, 1, NULL);
+	char *rev = RCS_getversion (finfo->rcs, tag, date, 1, NULL);
 	if (rev != NULL
 	    && !RCS_nodeisbranch (finfo->rcs, tag))
 	    nonbranch = 1;