MFC r277853

Check for invalid length or more than max length for the interpreter, instead
of the validity of the string pointer holding the interpreter.

Submitted by: sson

MFC r278827

Check for required arguments before accessing argv[0] and core dumping.

MFC r276419:

Move the explanation for examples before the example itself. Add
numerous QEMU examples and explanations supplied by sbruno, with thanks
to Ingo Schwarze for help with the mdoc markup. Code, text, testing,
proofreading, cinematography, stunts, and the haunting theme song
supplied by sbruno.

MFC r264269, r264282, r264280, r264291, r264276, r264314

Merge sson's binmiscctl and image activator features to stable/10

Submitted by: sson@freebsd.org

Add Stacey Son's binary activation patches that allow remapping of
execution to a emumation program via parsing of ELF header information.

With this kernel module and userland tool, poudriere is able to build
ports packages via the QEMU userland tools (or another emulator program)
in a different architecture chroot, e.g. TARGET=mips TARGET_ARCH=mips

I'm not connecting this to GENERIC for obvious reasons, but this should
allow the kernel module to be built by default and enable the building
of the userland tool (which automatically loads the kernel module).

Submitted by: sson@
Reviewed by: jhb@