Comment the use of System.gc in LocalDiskRepositoryTestCase

Change-Id: Ic5e9bda4275006ef3bf6ea6255ddf1c0eecc3770
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>

org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/LocalDiskRepositoryTestCase.java

@@ -119,6 +119,11 @@ public abstract class LocalDiskRepositoryTestCase extends TestCase {
 				shutdownHook = new Thread() {
 					@Override
 					public void run() {
+						// On windows accidentally open files or memory
+						// mapped regions may prevent files from being deleted.
+						// Suggesting a GC increases the likelihood that our
+						// test repositories actually get removed after the
+						// tests, even in the case of failure.
 						System.gc();
 						recursiveDelete("SHUTDOWN", trash, false, false);
 					}