Fix LockFileTest on Windows

LockFileTest was failing on Windows because we couldn't delete the lock
file of the index. The reason was that a LockFile instance still had an
open handle to the lock file preventing us to delete the file (in
contrast to the behavior on other platforms).

Change-Id: I1d50442b7eb8a27f98f69ad77c5e24a9698a7b66
Signed-off-by: Christian Halstrick <christian.halstrick@sap.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

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

@@ -70,13 +70,14 @@ public class LockFileTest extends RepositoryTestCase {
 		git.add().addFilepattern("file.txt").call();
 		assertNotNull(git.commit().setMessage("edit file").call());
 
-		assertTrue(new LockFile(db.getIndexFile(), db.getFS()).lock());
+		LockFile lf = new LockFile(db.getIndexFile(), db.getFS());
+		assertTrue(lf.lock());
 		try {
 			git.checkout().setName(commit1.name()).call();
 			fail("JGitInternalException not thrown");
 		} catch (JGitInternalException e) {
 			assertTrue(e.getCause() instanceof LockFailedException);
-			LockFile.unlock(((LockFailedException) e.getCause()).getFile());
+			lf.unlock();
 			git.checkout().setName(commit1.name()).call();
 		}
 	}