FileReftableStack: ensure new reftable files aren't missed on NFS

If "core.trustTablesListStat" is set to "after_open" to ensure file
attributes are refreshed on NFS refreshing only the attributes of the
tables.list file is not sufficient since then NFS may not detect new
reftable files (stored in the same refs/reftable/ directory) which may
cause FileNotFoundExceptions. Fix this by refreshing attributes of the
refs/reftable/ directory.

Change-Id: I7e07834fd7628a07ed644cb2740101a749d433bb

Author: msohn

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

@@ -314,9 +314,10 @@ boolean isUpToDate() throws IOException {
 				break;
 			case AFTER_OPEN:
 				try (InputStream stream = Files
-						.newInputStream(tablesListFile.toPath())) {
-					// open the tables.list file to refresh attributes (on some
-					// NFS clients)
+						.newInputStream(reftableDir.toPath())) {
+					// open the refs/reftable/ directory to refresh attributes
+					// of reftable files and the tables.list file listing their
+					// names (on some NFS clients)
 				} catch (FileNotFoundException | NoSuchFileException e) {
 					// ignore
 				}