Currently, this file has tsay() and nsay(), which are atomic vararg print operations
that are loud or quiet (respectively) during automated testing. These are used
throughout userland when output might get intermingled.
crash_prog was introduced to force-crash a userspace program
since _exit may not yet be implemented. However, the new versions
of OS161 already have the exact same logic as crash_prog in stdlib/exit.
and userspace.
In userspace, this is accessed through #include <secure.h>
In the kernel, this is access through #include <kern/secure.h>
There is a unit test for this (hm1) that computes the hmac and compares it to
the known value. The salted vesion tested offline.
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Also, fixed usespace compile issue with not changing KERNEL_SECRET => SECRET.
