missing "ThinkPad Extra Buttons" on ThinkPad X61

[Ben Liblit]

I wrote:
> The "thinkpad_acpi" kernel module is loaded.  However, the expected 
> "ThinkPad Extra Buttons" input source is missing:

The "thinkpad_acpi" module definitely detects the "ThinkPad Extra 
Buttons" feature:

	% cat /sys/class/input/input3/name
	ThinkPad Extra Buttons

There are eight "input*" subdirectories under "/sys/class/input", 
numbered input0 through input7.  Each of them appears in lshal with an 
"input.product" key *except* for this one.  lshal shows nothing 
mentioning input3 at all.

It's as though this one item were being filtered out for some mysterious 
reason.  Weird.  Any ideas?