Increase temporary buffer for unit test

Because we are using the large stream size, we have to be
above the STREAM_THRESHOLD constant, which I just increased.

Change-Id: I6f10ec8558d9f751d4b547fcae05af94f1c8866b
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

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

 		byte[] delta3 = tmp.toByteArray();
 		assertTrue(delta3.length > ObjectLoader.STREAM_THRESHOLD);
 
-		TemporaryBuffer.Heap pack = new TemporaryBuffer.Heap(64 * 1024);
+		TemporaryBuffer.Heap pack = new TemporaryBuffer.Heap(
+				ObjectLoader.STREAM_THRESHOLD + 1024);
 		packHeader(pack, 2);
 		objectHeader(pack, Constants.OBJ_BLOB, data0.length);
 		deflate(pack, data0);