[Java] Generalize dis-own native handle and refine dispose framework.

Summary:
1. Move disOwnNativeHandle() function from RocksDB to RocksObject
to allow other RocksObject to use disOwnNativeHandle() when its
ownership of native handle has been transferred.

2. RocksObject now has an abstract implementation of dispose(),
which does the following two things.  First, it checks whether
both isOwningNativeHandle() and isInitialized() return true.
If so, it will call the protected abstract function dispose0(),
which all the subclasses of RocksObject should implement.  Second,
it sets nativeHandle_ = 0.  This redesign ensure all subclasses
of RocksObject have the same dispose behavior.

3. All subclasses of RocksObject now should implement dispose0()
instead of dispose(), and dispose0() will be called only when
isInitialized() returns true.

Test Plan:
make rocksdbjava
make jtest

Reviewers: dhruba, sdong, ankgup87, rsumbaly, swapnilghike, zzbennett, haobo

Reviewed By: haobo

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D18801

java/org/rocksdb/ReadOptions.java

@@ -18,19 +18,6 @@ public class ReadOptions extends RocksObject {
   }
   private native void newReadOptions();
 
-  /**
-   * Release the memory allocated for the current instance
-   * in the c++ side.
-   *
-   * Calling other methods after dispose() leads to undefined behavior.
-   */
-  @Override public synchronized void dispose() {
-    if (isInitialized()) {
-      dispose(nativeHandle_);
-    }
-  }
-  private native void dispose(long handle);
-
   /**
    * If true, all data read from underlying storage will be
    * verified against corresponding checksums.
@@ -127,4 +114,12 @@ public class ReadOptions extends RocksObject {
   }
   private native void setTailing(
       long handle, boolean tailing);
+
+
+  @Override protected void disposeInternal() {
+    assert(isInitialized());
+    disposeInternal(nativeHandle_);
+  }
+  private native void disposeInternal(long handle);
+
 }