Speedup CleanFilter by transferring data in chunks of 8k

Transferring data byte per byte is slow, running add with CleanFilter on
a 2.9MB file takes 20 seconds. Using a buffer of 8k shrinks this time to
70ms.

Change-Id: I3bc2d8c11fe6cfaffcc99dc2a00643e01ac4e9cc
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.lfs/src/org/eclipse/jgit/lfs/CleanFilter.java

@@ -141,11 +141,12 @@ public class CleanFilter extends FilterCommand {
 
 	public int run() throws IOException {
 		try {
-			int b = in.read();
-			if (b != -1) {
-				dOut.write(b);
-				size++;
-				return 1;
+			byte[] buf = new byte[8192];
+			int length = in.read(buf);
+			if (length != -1) {
+				dOut.write(buf, 0, length);
+				size += length;
+				return length;
 			} else {
 				dOut.close();
 				tmpOut.close();