solution is to "disconnect" this from the libpng and libjpeg ports,
and fetch and extract them inside this port's own WRKDIR.
Note there are no shared library version problems because this port
doesn't link those libraries dynamically -- it just reaches into their
sources to compile some of its stuff. It is my belief that we
shouldn't have tried to share the WRKDIR with those two ports, as this
thing just too deeply depends on what's in their sources and the
relationship is thus not really a "dependency" in the regular sense.
Submitted by: mita@jp.freebsd.org (MITA Yoshio)
