MFC r272044:

Constify a parameter of name2oid.  No functional change.
MFC r274303:

Apply upstream 13597:3eac1e8e0f4c (git: illumos-gate@aa846ad9):

Initialize tqent_flags in the userland taskq implementation.  Without
this the assertion of tq->tq_freelist != NULL may fail in taskq_destroy.

The problem is that tqent_flags is never initialized in the userland
implementation while the kernel one does initialize it.  Without proper
initialization, the flag may have its lowest bit set, making it treated
as TQENT_FLAG_PREALLOC and never removing taskq_ent_t from tq_freelist.
MFC r274458,274523:

Derive copyright year from src/COPYRIGHT.
MFC r274276: MFV r274271:

Improve zdb -b performance:

 - Reduce gethrtime() call to 1/100th of blkptr's;
 - Skip manipulating the size-ordered tree;
 - Issue more (10, previously 3) async reads;
 - Use lighter weight testing in traverse_visitbp();

Illumos issue:
    5243 zdb -b could be much faster