Add alternate power changed event to acpithinkpad.c

[Brian Callahan]

Hi tech --

I just discovered that my Thinkpad (Edge E420) sends a 0x6040 event when 
the power cable is connected or removed.

Patch below handles it, works for me.

OK?

~Brian

Index: acpithinkpad.c
===================================================================
RCS file: /cvs/src/sys/dev/acpi/acpithinkpad.c,v
retrieving revision 1.29
diff -u -p -r1.29 acpithinkpad.c
--- acpithinkpad.c      22 Mar 2013 22:15:01 -0000      1.29
+++ acpithinkpad.c      31 Mar 2013 16:36:17 -0000
@@ -74,6 +74,7 @@
 #define        THINKPAD_TABLET_PEN_INSERTED    0x500b
 #define        THINKPAD_TABLET_PEN_REMOVED     0x500c
 #define        THINKPAD_POWER_CHANGED          0x6030
+#define        THINKPAD_POWER_CHANGED_ALT      0x6040
 #define        THINKPAD_BACKLIGHT_CHANGED      0x6050
 #define        THINKPAD_SWITCH_WIRELESS        0x7000

@@ -346,6 +347,7 @@ thinkpad_hotkey(struct aml_node *node, i
                        handled = 1;
                        break;
                case THINKPAD_POWER_CHANGED:
+               case THINKPAD_POWER_CHANGED_ALT:
                case THINKPAD_BACKLIGHT_CHANGED:
                        handled = 1;
                        break;