3006 VERIFY[S,U,P] and ASSERT[S,U,P] frequently check if first argument is zero

*** 19,30 ****
--- 19,35 ----
   * CDDL HEADER END
   */
  /*
   * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
+  *
   */
  
+ /*
+  * Copyright (c) 2012 by Delphix. All rights reserved.
+  */
+ 
  #include <sys/zfs_context.h>
  #include <sys/spa.h>
  #include <sys/dmu.h>
  #include <sys/zio.h>
  #include <sys/space_map.h>
*** 71,81 ****
  
  void
  space_map_destroy(space_map_t *sm)
  {
          ASSERT(!sm->sm_loaded && !sm->sm_loading);
!         VERIFY3U(sm->sm_space, ==, 0);
          avl_destroy(&sm->sm_root);
          cv_destroy(&sm->sm_load_cv);
  }
  
  void
--- 76,86 ----
  
  void
  space_map_destroy(space_map_t *sm)
  {
          ASSERT(!sm->sm_loaded && !sm->sm_loading);
!         VERIFY0(sm->sm_space);
          avl_destroy(&sm->sm_root);
          cv_destroy(&sm->sm_load_cv);
  }
  
  void
*** 284,294 ****
          sm->sm_loading = B_TRUE;
          end = smo->smo_objsize;
          space = smo->smo_alloc;
  
          ASSERT(sm->sm_ops == NULL);
!         VERIFY3U(sm->sm_space, ==, 0);
  
          if (maptype == SM_FREE) {
                  space_map_add(sm, sm->sm_start, sm->sm_size);
                  space = sm->sm_size - space;
          }
--- 289,299 ----
          sm->sm_loading = B_TRUE;
          end = smo->smo_objsize;
          space = smo->smo_alloc;
  
          ASSERT(sm->sm_ops == NULL);
!         VERIFY0(sm->sm_space);
  
          if (maptype == SM_FREE) {
                  space_map_add(sm, sm->sm_start, sm->sm_size);
                  space = sm->sm_size - space;
          }
*** 473,483 ****
                  smo->smo_objsize += size;
          }
  
          zio_buf_free(entry_map, bufsize);
  
!         VERIFY3U(sm->sm_space, ==, 0);
  }
  
  void
  space_map_truncate(space_map_obj_t *smo, objset_t *os, dmu_tx_t *tx)
  {
--- 478,488 ----
                  smo->smo_objsize += size;
          }
  
          zio_buf_free(entry_map, bufsize);
  
!         VERIFY0(sm->sm_space);
  }
  
  void
  space_map_truncate(space_map_obj_t *smo, objset_t *os, dmu_tx_t *tx)
  {