swapon - Implement encrypted swap
Implement crypting of the swap device. When enabled in this manner
/dev/urandom is used to generate a 256-bit random key and the base device
is automatically cryptsetup and mapped, making crypted swap trivial.
* Implement the 'crypt' fstab option, so swapon -a and swapoff -a work
as expected for crypted swap. Again, the base device (e.g. /dev/da0s1b)
should be specified. The option will automatically map it with cryptsetup
and swap on the mapping.
Also implement -c to crypt manual swapon/swapoff commands. If used for
swapon it must also be used for swapoff. Again, specify the base device
(e.g. /dev/da0s1b), not the /dev/mapper device, for both cases.
* Implement the 'trim' fstab option, allow trim to be specified in the fstab
instead of requiring a rc.conf option.
* The trim option no longer exits with an error if the device does not
support TRIM or TRIM is not enabled.