Make RepoProject#setUpstream public

Applications using JGit such as Gerrit plugins may have their own
manifest parsers. They can start using RepoProject to some extent
with this change. Eventually, they can be migrated to use the
ManifestParser in JGit, however until then, this change can help
make the migration incremental.

Change-Id: I6a32d4f4622c3842eedf7873cdfed2f1ca998f6f
(cherry picked from commit e3e0a1ea)

org.eclipse.jgit/src/org/eclipse/jgit/gitrepo/RepoProject.java

@@ -411,7 +411,7 @@ public String getUpstream() {
 	 *
 	 * @since 6.10
 	 */
-	void setUpstream(String upstream) {
+	public void setUpstream(String upstream) {
 		this.upstream = upstream;
 	}