Use java.nio to delete path to get detailed errors

Get the full IOException of the reason why a directory
cannot be removed during GC.

Change-Id: Ia555bce009fa48087a73d677f1ce3b9c0b685b57
Signed-off-by: Luca Milanesio <luca.milanesio@gmail.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

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

@@ -884,7 +884,7 @@ public class GC {
 	}
 
 	private void deleteEmptyRefsFolders() throws IOException {
-		Path refs = repo.getDirectory().toPath().resolve("refs"); //$NON-NLS-1$
+		Path refs = repo.getDirectory().toPath().resolve(Constants.R_REFS);
 		try (Stream<Path> entries = Files.list(refs)) {
 			Iterator<Path> iterator = entries.iterator();
 			while (iterator.hasNext()) {
@@ -908,7 +908,7 @@ public class GC {
 		return p.toFile().isDirectory();
 	}
 
-	private boolean delete(Path d) {
+	private void delete(Path d) {
 		try {
 			// Avoid deleting a folder that was just created so that concurrent
 			// operations trying to create a reference are not impacted
@@ -918,12 +918,12 @@ public class GC {
 				// If the folder is not empty, the delete operation will fail
 				// silently. This is a cheaper alternative to filtering the
 				// stream in the calling method.
-				return d.toFile().delete();
+				Files.delete(d);
 			}
 		} catch (IOException e) {
-			LOG.error(e.getMessage(), e);
+			LOG.error(MessageFormat.format(JGitText.get().cannotDeleteFile, d),
+					e);
 		}
-		return false;
 	}
 
 	/**