Pages with '?' in their name break links in the web interface.

The proper solution is maybe to generate links that are
properly url-encoded, that would remove the limitations on <>
too, but url-encoding is trickier than it seems.

But for now it's easier to just keep people from creating
such pages.

Reference: /n/sources/patch/applied/wikifs-not-allow-questionmark-in-title
Date: Tue Dec 13 09:42:11 CET 2005

--- /sys/src/cmd/wikifs/io.c	Tue Dec 13 09:33:06 2005
+++ /sys/src/cmd/wikifs/io.c	Tue Dec 13 09:33:02 2005
@@ -445,7 +445,7 @@
 		return -1;
 	}
 
-	if(title[0]=='\0' || strpbrk(title, "/<>:")){
+	if(title[0]=='\0' || strpbrk(title, "/<>:?")){
 		werrstr("invalid character in name");
 		return -1;
 	}