MFC r256343,256540-256541,256544,256549,256551,256553,257939,258021,258927,
259144,259148,259470,259472,259474,259476-259478,259480-259481,259570,
259597-259598, and 261960 (24 revisions; summarized below)...
r256343: Add zfsboot module as an option for automatic configuration
r256540: Add zpool_cache_* variables to loader.conf(5)
r256541: Document BSDINSTALL_TMPBOOT in bsdinstall.8
r256544: Fix a typo when setting up loader.conf(5) GELI entries
r256549: Document zfsboot in bsdinstall.8
r256551: Bump .Dd date in bsdinstall.8
r256553: Align ZFSBOOT_BEROOT_NAME with sysutils/beadm + Solaris beadm
r257939: Validate scripted partition entry before acting on disks
r258021: Switch default MBR bootcode from /boot/boot0 to /boot/mbr
r258927: Fix early regression in enabling the Encryption feature
r259144: Fix early regression in entering passphrase for Encryption
r259148: Fix typo that broke booting from Encrypted setup
r259470: Add default /var/mail with atime=on for mail apps
r259472: Accept NULL input as also meaning zero swap
r259474: Bug fixes and debugging improvements
r259476: Improve default ZFS disk layout
r259477: fletcher4 is currently the default
r259478: De-uglify the geli(8)-setup infobox by adding a newline
r259480: Fix ghosted zroot pool issue
r259481: Auto-enable 4k alignment with Encryption
r259570: Fix "[: -eq: argument expected" error
r259597: Fix installation to 3-4+ disks
r259598: Set the cachefile property so bootpools get imported
r261960: Add zfsboot to scripted interface of bsdinstall