Bump to latest pom-imagej

Increased pom version to 2.38
LegacyOpener: attach slice labels to the stack, if any were found

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add a regression test for loading images with slice labels

This bug in our SCIFIO adapter was noticed and reported by Bob Dougherty:
http://thread.gmane.org/gmane.comp.java.imagej/33423/

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

The use of "SliceLabels" is a hack, and must be documented as such.