Make ObjectToPack clearReuseAsIs signal available to subclasses

A subclass may want to use this method to release handles that are
caching reuse information.  Make it protected so they can override
it and update themselves.

Change-Id: I2277a56ad28560d2d2d97961cbc74bc7405a70d4
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit/src/org/eclipse/jgit/storage/file/LocalObjectToPack.java

@@ -62,6 +62,12 @@ class LocalObjectToPack extends ObjectToPack {
 		super(obj);
 	}
 
+	@Override
+	protected void clearReuseAsIs() {
+		super.clearReuseAsIs();
+		pack = null;
+	}
+
 	@Override
 	public void select(StoredObjectRepresentation ref) {
 		LocalObjectRepresentation ptr = (LocalObjectRepresentation) ref;

org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/ObjectToPack.java

@@ -199,7 +199,14 @@ public class ObjectToPack extends PackedObjectInfo {
 		flags |= REUSE_AS_IS;
 	}
 
-	void clearReuseAsIs() {
+	/**
+	 * Forget the reuse information previously stored.
+	 * <p>
+	 * Implementations may subclass this method, but they must also invoke the
+	 * super version with {@code super.clearReuseAsIs()} to ensure the flag is
+	 * properly cleared for the writer.
+	 */
+	protected void clearReuseAsIs() {
 		flags &= ~REUSE_AS_IS;
 	}