Make display blank faster after dismissing an alarm

Having display stay on 2.5 seconds after dismissing an alarm was
felt too long by many users. Also since power key is reserved for
snoozing alarm until the dialog is gone, people have learned a
habit of repeatedly pressing the power key until display actually
blanks - which can trigger reset proximity state via triple power
key press.

Shorten the display on time after alarm to 1.25 seconds.

Users that are not pleased with the new default value can use
mcetool to select a custom time value - for example 1 second:

  mcetool --set-exception-length-alarm=1000

[mce] Make display blank faster after dismissing an alarm. Fixes JB#28552

tklock.h

@@ -153,7 +153,7 @@ enum
 
 /** How long to keep display on after alarm is handled [ms] */
 #define MCE_GCONF_EXCEPTION_LENGTH_ALARM        MCE_GCONF_LOCK_PATH"/exception_length_alarm"
-#define DEFAULT_EXCEPTION_LENGTH_ALARM          2500
+#define DEFAULT_EXCEPTION_LENGTH_ALARM          1250
 
 /** How long to keep display on when usb cable is connected [ms] */
 #define MCE_GCONF_EXCEPTION_LENGTH_USB_CONNECT  MCE_GCONF_LOCK_PATH"/exception_length_usb_connect"