4171 clean up spa_feature_*() interfaces
4172 implement extensible_dataset feature for use by other zpool features
Reviewed by: Max Grossman <max.grossman@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>

*** 20,30 ****
   */
  
  /*
   * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
   * Copyright 2011 Nexenta Systems, Inc. All rights reserved.
!  * Copyright (c) 2012 by Delphix. All rights reserved.
   * Copyright (c) 2012 by Frederik Wessels. All rights reserved.
   * Copyright (c) 2013 by Prasad Joshi (sTec). All rights reserved.
   */
  
  #include <assert.h>
--- 20,30 ----
   */
  
  /*
   * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
   * Copyright 2011 Nexenta Systems, Inc. All rights reserved.
!  * Copyright (c) 2013 by Delphix. All rights reserved.
   * Copyright (c) 2012 by Frederik Wessels. All rights reserved.
   * Copyright (c) 2013 by Prasad Joshi (sTec). All rights reserved.
   */
  
  #include <assert.h>
*** 874,884 ****
          } else {
                  /*
                   * Hand off to libzfs.
                   */
                  if (enable_all_pool_feat) {
!                         int i;
                          for (i = 0; i < SPA_FEATURES; i++) {
                                  char propname[MAXPATHLEN];
                                  zfeature_info_t *feat = &spa_feature_table[i];
  
                                  (void) snprintf(propname, sizeof (propname),
--- 874,884 ----
          } else {
                  /*
                   * Hand off to libzfs.
                   */
                  if (enable_all_pool_feat) {
!                         spa_feature_t i;
                          for (i = 0; i < SPA_FEATURES; i++) {
                                  char propname[MAXPATHLEN];
                                  zfeature_info_t *feat = &spa_feature_table[i];
  
                                  (void) snprintf(propname, sizeof (propname),