fixup??? Add reftable library

Close files before trying to unlink them. This is actually required on
Windows.

Note: this is probably not the only part of the code that requires this
type of fix, but it seems to be enough to let the _current_ version of
t0031 pass.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

reftable/stack.c

@@ -884,6 +884,10 @@ static int stack_compact_range(struct reftable_stack *st, int first, int last,
 		}
 	}
 
+	if (lock_file_fd > 0) {
+		close(lock_file_fd);
+		lock_file_fd = 0;
+	}
 	err = unlink(slice_as_string(&lock_file_name));
 	if (err < 0) {
 		goto exit;