MFC r315595,r315601,r315603,r315647:

r315595:

Remove a commented out line before kvm_getprocs(3)

The commented out return value for kvm_getprocs(3) was misleading -- the
uncommented line is correct.

No content change

r315601:

kvm_open2(3): remove '*' when describing addr argument for resolver

As noted by vangyzen, with a similar issue in D10022, the pointer portion of
the .Fa macro call is unnecessary, so remove the '*'.

r315603:

kvm_close(3): return error instead of blindly returning 0

error is the accumulated error from previous close(2) calls.

This bug has been present since the libcall's import from 4.4BSD
Lite (r1573).

Noticed by: vangyzen (D10022)
Relnotes: yes

r315647:

Handle kd == NULL gracefully with kvm_close(3)

Don't segfault in kvm_close(3) if provided a NULL pointer. Instead, return
-1 and set errno to EINVAL.

Document this new behavior explicitly.