Fix various security related issues:

    0001. Do not recognize paths, mail folders, and pipes in mail addresses
    by default.  That avoids a direct command injection with syntactically
    valid email addresses starting with |.

    Such addresses can be specified both on the command line, the mail
    headers (with -t) or in address lines copied over from previous
    while replying.

    This was assigned CVE-2014-7844 for some versions of BSD mailx.  It is
    documented behavior for Heirloom mailx, and was mentioned in an old
    technical report about BSD mailx (which does not usually make its way
    into operating system installations).  The patch switches off this
    processing and updates the documentation.

Added expandaddr option to explicitly enable this behavior.

    0002. When invoking sendmail, prevent option processing for email
    address arguments.  This prevents changing e.g. the Postfix
    configuration file in unexpected ways.  This behavior was documented for
    BSD mailx (sort of), but not for Heirloom mailx.  We did not assign a
    CVE to this because it is more of a missing feature, and code invoking
    mailx needs adjustment in the caller as well.

Fixed.

    0003. Make wordexp support mandatory.  (No functional change.)

Fixed (replaced explicit shell pipe implementation).

    0004. Prevent command execution in the expand function, which is IMHO
    unexpected.  (Not really required with patch 1, and there is still
    information disclosure/DoS potential if this expansion occurs.)  This is
    a historic vulnerability already fixed in the Debian package,
    retroactively assigned CVE-2004-2771:

Fixed (as part of the pipe replacement with wordexp).
Allow for arbitrary MI scheduler implementations.

A concrete result is enabling unpatched libpthread to run on the
rumprun stacks (e.g. Xen and bare metal) with a non-NetBSD scheduler.
Those schedulers hook into the existing _lwp_frobnitz() NetBSD syscall
interfaces (well, "syscall" interfaces in that scenario ;)

More specifically about the change itself:

1) instead of calling _lwp_makecontext() followed by _lwp_create()
   and passing the entry point in ucontext_t (MD) through the calls, roll
   the calls into pthread__makelwp() and allow alternate implementations
   for that MI interface.

2) allow compile-time overriding of __lwp_gettcb_fast() or
   __lwp_getprivate_fast, which are inline and leak MD scheduler/thread
   details into libpthread

Additionally, two small nits:

I)  define LIB=pthread before including mk.conf so that it's possible
    to test for LIB==pthread in mk.conf

II) make it possible to leave out pthread_cancelstub.c.  This is required
    by the current implementation of rumprun-posix (i.e. rumprun on
    POSIX hosts) due to symbol collisions.  It needs to be fixed properly
    some day, but for now allows an almost-correct libpthread to run.
    I am sure @justin will be happy to explain the details ;)

no change to NetBSD
tested: anita+atf
first draft of a driver for SMSI,mgx
More or less an Alliance Semiconductors ProMotion AT24 with some PCI-SBus
glue and 4MB framebuffer. No acceleration yet, just enough wsdisplay/vcons
setup and DAC programming to be functional.