Make Repository.shortenRefName static

The method has no reason to be non-static.

Change-Id: I1c09e074395d49cee0e6e53679b499d1f0c351ea

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/Branch.java

@@ -150,7 +150,7 @@ class Branch extends TextBuiltin {
 					startBranch = startRef.getName();
 				else
 					startBranch = startAt.name();
-				startBranch = db.shortenRefName(startBranch);
+				startBranch = Repository.shortenRefName(startBranch);
 				String newRefName = newHead;
 				if (!newRefName.startsWith(Constants.R_HEADS))
 					newRefName = Constants.R_HEADS + newRefName;

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

@@ -77,14 +77,13 @@ public abstract class RefRename {
 		source = src;
 		destination = dst;
 
-		Repository repo = destination.getRepository();
 		String cmd = "";
 		if (source.getName().startsWith(Constants.R_HEADS)
 				&& destination.getName().startsWith(Constants.R_HEADS))
 			cmd = "Branch: ";
 		setRefLogMessage(cmd + "renamed "
-				+ repo.shortenRefName(source.getName()) + " to "
-				+ repo.shortenRefName(destination.getName()));
+				+ Repository.shortenRefName(source.getName()) + " to "
+				+ Repository.shortenRefName(destination.getName()));
 	}
 
 	/** @return identity of the user making the change in the reflog. */

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

@@ -1119,7 +1119,7 @@ public abstract class Repository {
 	 *
 	 * @return a more user friendly ref name
 	 */
-	public String shortenRefName(String refName) {
+	public static String shortenRefName(String refName) {
 		if (refName.startsWith(Constants.R_HEADS))
 			return refName.substring(Constants.R_HEADS.length());
 		if (refName.startsWith(Constants.R_TAGS))