Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Add initial tests for stat(1)

Testcases for -H, -L, and -f haven't been implemented yet, in part due
to additional complexity needed to validate the features:
* -H and -f will require an external "helper" program to display/modify
the state/permissions for a given path.
* -L is being covered partially via the -n testcase today.

MFC after: 1 month

Write up some basic tests for readlink(1)

The tests exercise -f (f_flag), -n (n_flag), and no arguments (basic).

MFC after: 1 month
Sponsored by: Dell EMC Isilon