Expose FileStoreAttributes.setBackground()

The FS.setAsyncFileStoreAttributes() static method calls
FileStoreAttributes.setBackground() as its implementation, but there are
other public attributes on this inner class already and there isn't a
real reason why this needs to be private.

By making it public we allow callers to be able to invoke it directly.
Although it doesn't appear that it would make a difference, by calling a
static method on the FS class, all static fields and the transitive
closure of class dependencies must be loaded and initialised, which can
be non-trivial.

Callers referring to FS.setAsyncFileStoreAttributes() may be replaced
with FS.FileStoreAttributes.setBackground() with no change of behaviour
other than improved performance due to less class loading required.

Bug: 560527
Change-Id: I9538acc90da8d18f53fd60d74eb54496857f93a5
Signed-off-by: Alex Blewitt <alex.blewitt@gmail.com>

org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java

@@ -242,7 +242,16 @@ public abstract class FS {
 
 		private static Map<FileStore, Lock> locks = new ConcurrentHashMap<>();
 
-		private static void setBackground(boolean async) {
+		/**
+		 * Whether FileStore attributes should be determined asynchronously
+		 *
+		 * @param async
+		 *            whether FileStore attributes should be determined
+		 *            asynchronously. If false access to cached attributes may block
+		 *            for some seconds for the first call per FileStore
+		 * @since 5.6.2
+		 */
+		public static void setBackground(boolean async) {
 			background.set(async);
 		}
 
@@ -709,7 +718,9 @@ public abstract class FS {
 	 *            asynchronously. If false access to cached attributes may block
 	 *            for some seconds for the first call per FileStore
 	 * @since 5.1.9
+	 * @deprecated Use {@link FileStoreAttributes#setBackground} instead
 	 */
+	@Deprecated
 	public static void setAsyncFileStoreAttributes(boolean asynch) {
 		FileStoreAttributes.setBackground(asynch);
 	}