SF 3435567

Possibility to pass a NULL Dispatch pointer
Fix a memory leak (detected with Glowcode) in Variant.cpp/zeroVariant function
Variant.toString improvement to handle NULL cases
Adds the error code to the message when "an unknown COM error has occurred"
Added debug info to EventProxy advise registration failure message.

unittest/com/jacob/com/VariantTest.java

@@ -701,4 +701,17 @@ public class VariantTest extends BaseTestCase {
 			// yeah! can't get dispatch from boolean
 		}
 	}
+
+	/**
+	 * Verify SF 3435567 null and empty behavior change
+	 */
+	public void testGetNullString() {
+		Variant testVariant = new Variant();
+		testVariant.putNull();
+		assertNull(testVariant.getString());
+		testVariant.putEmpty();
+		assertNull(testVariant.getString());
+		testVariant.putString("dog");
+		assertEquals("dog", testVariant.getString());
+	}
 }