update to 4.2r4
changes:
-API additions
-hdp and hrepack utilities can now display more compression information
-build system updates
-bugfixes

pkgsrc notes:
-we build shared libraries now although it is officially unsupported
if Fortran is enabled (works for me)
-The 24-bit-jpeg selftest fails. It also failed with the previous
version. (perhaps jpeg-7 related?) The test contains too much magic
to tell what happens.

(drochner)