avcodec/x86/vp9dsp: use EXTERNAL_* macros.

Original fix by one of these developers:
    Anton Khirnov <anton@khirnov.net>
    Diego Biurrun <diego@biurrun.de>
    Luca Barbato <lu_zero@gentoo.org>
    Martin Storsjö <martin@martin.st>

See 97962b2 / 72ca830

Personnal guess is Diego Biurrun.
avcodec/vp9: make last_invisible local.

Original change by one of these developers:
    Anton Khirnov <anton@khirnov.net>
    Diego Biurrun <diego@biurrun.de>
    Luca Barbato <lu_zero@gentoo.org>
    Martin Storsjö <martin@martin.st>

See 97962b2 / 72ca830
vp9: Ensure that the arithmetic coder values are read in the right order

The operands of an addition can be evaluated in any order, since
the addition isn't a sequence point. The only operators that
have a defined evaluation order are &&, ||, ?: and the sequence
operator ','.

This fixes fate-vp9 on ARM RVCT.
swscale/swscale_unscaled: fix right column handling in planarCopyWrapper

Found-by: Михаил <Micky53@mail.ru>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>