Fix 2447470: always update the battery status when it's below the threshold.

Previously, the battery percentage was only shown when the battery level
transitioned below the LOW_BATTERY_THRESHOLD (20%).  This change makes it so it gets updated
whenever we get a battery status update where the level is below LOW_BATTERY_THRESHOLD.

Note: this only applies to the pattern unlock screen.
diff --git a/policy/com/android/internal/policy/impl/KeyguardUpdateMonitor.java b/policy/com/android/internal/policy/impl/KeyguardUpdateMonitor.java
index b7187a4..b7bb184 100644
--- a/policy/com/android/internal/policy/impl/KeyguardUpdateMonitor.java
+++ b/policy/com/android/internal/policy/impl/KeyguardUpdateMonitor.java
@@ -385,14 +385,8 @@
         }
 
         if (!pluggedIn) {
-            // not plugged in and going below threshold
-            if (batteryLevel < LOW_BATTERY_THRESHOLD
-                    && mBatteryLevel >= LOW_BATTERY_THRESHOLD) {
-                return true;
-            }
-            // not plugged in and going above threshold (sounds impossible, but, meh...)
-            if (mBatteryLevel < LOW_BATTERY_THRESHOLD
-                    && batteryLevel >= LOW_BATTERY_THRESHOLD) {
+            // not plugged in and below threshold
+            if (batteryLevel < LOW_BATTERY_THRESHOLD && batteryLevel != mBatteryLevel) {
                 return true;
             }
         }