Rename extensions.refsStorage to refStorage

This matches the proposal that has been discussed at length on
git-core mailing list and seems to be the accepted convention.

Change-Id: I9f6ab15144826893d1e2a4b48a2d657d6dd445ec

org.eclipse.jgit.pgm/resources/org/eclipse/jgit/pgm/internal/CLIText.properties

@@ -257,7 +257,7 @@ usage_PrunePreserved=Remove the preserved subdirectory containing previously pre
 usage_ReadDirCache= Read the DirCache 100 times
 usage_RebuildCommitGraph=Recreate a repository from another one's commit graph
 usage_RebuildRefTree=Copy references into a RefTree
-usage_RebuildRefTreeEnable=set extensions.refsStorage = reftree
+usage_RebuildRefTreeEnable=set extensions.refStorage = reftree
 usage_Remote=Manage set of tracked repositories
 usage_RepositoryToReadFrom=Repository to read from
 usage_RepositoryToReceiveInto=Repository to receive into

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/debug/RebuildRefTree.java

@@ -133,7 +133,7 @@ class RebuildRefTree extends TextBuiltin {
 			if (enable && !(db.getRefDatabase() instanceof RefTreeDatabase)) {
 				StoredConfig cfg = db.getConfig();
 				cfg.setInt("core", null, "repositoryformatversion", 1); //$NON-NLS-1$ //$NON-NLS-2$
-				cfg.setString("extensions", null, "refsStorage", "reftree"); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
+				cfg.setString("extensions", null, "refStorage", "reftree"); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
 				cfg.save();
 				errw.println("Enabled reftree."); //$NON-NLS-1$
 				errw.flush();

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/reftree/LocalDiskRefTreeDatabaseTest.java

@@ -83,7 +83,7 @@ public class LocalDiskRefTreeDatabaseTest extends LocalDiskRepositoryTestCase {
 		FileRepository init = createWorkRepository();
 		FileBasedConfig cfg = init.getConfig();
 		cfg.setInt("core", null, "repositoryformatversion", 1);
-		cfg.setString("extensions", null, "refsStorage", "reftree");
+		cfg.setString("extensions", null, "refStorage", "reftree");
 		cfg.save();
 
 		repo = (FileRepository) new FileRepositoryBuilder()

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileRepository.java

@@ -216,7 +216,7 @@ public class FileRepository extends Repository {
 				ConfigConstants.CONFIG_KEY_REPO_FORMAT_VERSION, 0);
 
 		String reftype = repoConfig.getString(
-				"extensions", null, "refsStorage"); //$NON-NLS-1$ //$NON-NLS-2$
+				"extensions", null, "refStorage"); //$NON-NLS-1$ //$NON-NLS-2$
 		if (repositoryFormatVersion >= 1 && reftype != null) {
 			if (StringUtils.equalsIgnoreCase(reftype, "reftree")) { //$NON-NLS-1$
 				refs = new RefTreeDatabase(this, new RefDirectory(this));