Fix HBase mutateMany

EntryList/Buffer refactoring caused a map used by HBase's mutateMany
to call get with objects never equal to those used in calls to put.
The bug manifested like this:

mutateManyWritesSameKeyOnMultipleCFs(com.thinkaurelius.titan.diskstorage.hbase.HBaseMultiWriteKeyColumnValueStoreTest)  Time elapsed: 19.315 sec  <<< FAILURE!
java.lang.AssertionError: expected:<[  0-  0-  0-  0-  0-  0-  0- 42-> 0-  0-  0-  0-  0-  1- 33-104]> but was:<[]>
        at org.junit.Assert.fail(Assert.java:88)
        at org.junit.Assert.failNotEquals(Assert.java:743)
        at org.junit.Assert.assertEquals(Assert.java:118)
        at org.junit.Assert.assertEquals(Assert.java:144)
        at com.thinkaurelius.titan.diskstorage.MultiWriteKeyColumnValueStoreTest.mutateManyWritesSameKeyOnMultipleCFs(MultiWriteKeyColumnValueStoreTest.java:167)