Make PrePushHook properly terminate ref lines

All of the input lines passed to pre-push hook scripts must be properly
terminated by '\n', so that normal shell scripts like the git-supplied
pre-push.sample work properly, even when pushing just a single branch.

With the old code, hook scripts that use the following pattern didn't
process the last line, because 'read' has a non-zero exit status when
EOF is encountered:
  while read local_ref local_sha remote_ref remote_sha; do ... done

Change-Id: Id899662ed3fedef6c314fc4b2ddf91a6dcb98cbb
Signed-off-by: Markus Keller <markus.kell.r@gmail.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/api/PushCommandTest.java

 			git1.push().setRemote("test").setRefSpecs(spec).call();
 			assertEquals("1:test, 2:" + uri + ", 3:\n" + "refs/heads/master "
 					+ commit.getName() + " refs/heads/x "
-					+ ObjectId.zeroId().name(), read(hookOutput));
+					+ ObjectId.zeroId().name() + "\n", read(hookOutput));
 		}
 	}
 

org.eclipse.jgit/src/org/eclipse/jgit/hooks/PrePushHook.java

 	 */
 	public void setRefs(Collection<RemoteRefUpdate> toRefs) {
 		StringBuilder b = new StringBuilder();
-		boolean first = true;
 		for (RemoteRefUpdate u : toRefs) {
-			if (!first)
-				b.append("\n"); //$NON-NLS-1$
-			else
-				first = false;
 			b.append(u.getSrcRef());
 			b.append(" "); //$NON-NLS-1$
 			b.append(u.getNewObjectId().getName());
 			ObjectId ooid = u.getExpectedOldObjectId();
 			b.append((ooid == null) ? ObjectId.zeroId().getName() : ooid
 					.getName());
+			b.append("\n"); //$NON-NLS-1$
 		}
 		refs = b.toString();
 	}