SPARK-1611: Fix incorrect initialization order in AppendOnlyMap

JIRA: https://issues.apache.org/jira/browse/SPARK-1611

Author: zsxwing <zsxwing@gmail.com>

Closes #534 from zsxwing/SPARK-1611 and squashes the following commits:

96af089 [zsxwing] SPARK-1611: Fix incorrect initialization order in AppendOnlyMap

core/src/main/scala/org/apache/spark/util/collection/AppendOnlyMap.scala

@@ -40,6 +40,8 @@ class AppendOnlyMap[K, V](initialCapacity: Int = 64)
   require(initialCapacity <= (1 << 29), "Can't make capacity bigger than 2^29 elements")
   require(initialCapacity >= 1, "Invalid initial capacity")
 
+  private val LOAD_FACTOR = 0.7
+
   private var capacity = nextPowerOf2(initialCapacity)
   private var mask = capacity - 1
   private var curSize = 0
@@ -57,8 +59,6 @@ class AppendOnlyMap[K, V](initialCapacity: Int = 64)
   private var destroyed = false
   private val destructionMessage = "Map state is invalid from destructive sorting!"
 
-  private val LOAD_FACTOR = 0.7
-
   /** Get the value for a given key */
   def apply(key: K): V = {
     assert(!destroyed, destructionMessage)