Cache filemode in GitIndex

Apparently this was the intention, but never happened

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

org.eclipse.jgit/src/org/eclipse/jgit/lib/GitIndex.java

@@ -353,7 +353,8 @@ public class GitIndex {
 		if (filemode != null)
 			return filemode.booleanValue();
 		RepositoryConfig config = db.getConfig();
-		return config.getBoolean("core", null, "filemode", true);
+		filemode = Boolean.valueOf(config.getBoolean("core", null, "filemode", true));
+		return filemode.booleanValue();
 	}
 
 	/** An index entry */