[Midnightbsd-cvs] mports: graphics/png: use xz

[laffer1 at midnightbsd.org]

Log Message:
-----------
use xz

Modified Files:
--------------
    mports/graphics/png:
        Makefile (r1.19 -> r1.20)
        (http://cvsweb.midnightbsd.org/mports/graphics/png/Makefile?r1=1.19&r2=1.20)
        distinfo (r1.13 -> r1.14)
        (http://cvsweb.midnightbsd.org/mports/graphics/png/distinfo?r1=1.13&r2=1.14)