Fix unstable test

Add more time to a timestamp to safely go beyond the granularity of
the timestamp resolution of the file system. The lowest resolution we
know of is FAT with two second resolution. Then add some to make sure we
are above the limit.

Change-Id: I85c5b07dcdf2d80de41fe9b2354ccc888bad7f1e

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

@@ -321,7 +321,7 @@ public class CommitCommandTest extends RepositoryTestCase {
 		db.getIndexFile().setLastModified(indexTime - 5000);
 
 		write(file1, "content4");
-		assertTrue(file1.setLastModified(file1.lastModified() + 1000));
+		assertTrue(file1.setLastModified(file1.lastModified() + 2500));
 		assertNotNull(git.commit().setMessage("edit file").setOnly("file1.txt")
 				.call());