illumos gate

It would be useful if digest would be able to automatically verify checksum by reading from a file. The compatibility with tools from GNU (e.g. sha*sum/md5sum..) should be used optional. FreeBSD tools (sha*/md5) have "-r", which make them compatible with GNU format.

Example:

$ root@userland:/root# sha256sum file > file.sha256sum
$ root@userland:/root# sha256sum -c file.sha256sum 
file: OK
$ root@userland:/root# digest -a sha256 -v file > file.sha256
$ root@userland:/root# digest -c file.sha256
file: OK
$ root@userland:/root# digest -r -c file.sha256sum
file: OK