Hide deprecation warnings in some test classes

These test classes heavily rely on Tree and associated classes. They
are convenient for building test cases and hence not yet replaced, but
there is a deprecation warning at about every line, which is not helpful.

Change-Id: Ia7cc8f3bb980dc03055b94748b6c7529a82ea5a5

org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/IndexDiffTest.java

@@ -70,6 +70,7 @@ import org.eclipse.jgit.treewalk.FileTreeIterator;
 import org.eclipse.jgit.util.IO;
 import org.junit.Test;
 
+@SuppressWarnings("deprecation")
 public class IndexDiffTest extends RepositoryTestCase {
 
 	static PathEdit add(final Repository db, final File workdir,

org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/T0002_TreeTest.java

@@ -57,6 +57,7 @@ import java.util.List;
 
 import org.junit.Test;
 
+@SuppressWarnings("deprecation")
 public class T0002_TreeTest extends SampleDataRepositoryTestCase {
 	private static final ObjectId SOME_FAKE_ID = ObjectId.fromString(
 			"0123456789abcdef0123456789abcdef01234567");

org.eclipse.jgit.test/tst/org/eclipse/jgit/revwalk/ObjectWalkTest.java

@@ -54,6 +54,7 @@ import org.eclipse.jgit.lib.ObjectInserter;
 import org.eclipse.jgit.lib.Tree;
 import org.junit.Test;
 
+@SuppressWarnings("deprecation")
 public class ObjectWalkTest extends RevWalkTestCase {
 	protected ObjectWalk objw;
 

org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/T0003_BasicTest.java

@@ -84,6 +84,7 @@ import org.eclipse.jgit.revwalk.RevWalk;
 import org.eclipse.jgit.util.FileUtils;
 import org.junit.Test;
 
+@SuppressWarnings("deprecation")
 public class T0003_BasicTest extends SampleDataRepositoryTestCase {
 
 	@Test