Avoid exec:exec hack

To be able to load the native library, we introduced a hack to fork
a new Java process with a hand-crafted java.library.path. But that
system was not flexible enough: it only worked for the same platform
as it was developed on. So let's not go the NarSystem route but do
something slightly more clever.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Remove debug output

Logging every pixel access to stderr is really, really slow...

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Provide a real ImgFactory

VigraImgFactory2DUnsignedByte should be a real ImgFactory; after all,
the medium-term goal is to pass it to SCIFIO's ImgOpener.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>