MFC r264669: MFV r264666:

4374 dn_free_ranges should use range_tree_t

illumos/illumos-gate@bf16b11e8deb633dd6c4296d46e92399d1582df4
MFC r264671 (MFV r264668):

4754 io issued to near-full luns even after setting noalloc threshold
4755 mg_alloc_failures is no longer needed

illumos/illumos@b6240e830b871f59c22a3918aebb3b36c872edba
MFC r264740:

Use case insensitive match in portsnap.

PR:		bin/186510
Submitted by:	olli
MFC r264835 (MFV r264829):

3897 zfs filesystem and snapshot limits
MFC r264836 (MFV r264830):

4745 fix AVL code misspellings