Probe for shaded jars with parsing Maven poms.
Add m: prefix when reading extra attributes from resolution cache.

Without this, the hashCode of MDArtifact and DefaultArtifact will
be different for artifacts with a Maven classifier.

In particular, this led to artifacts with classifiers not being put
on the IvyDE classpath.
Merge branch 'probe_shaded' into bizo

* probe_shaded:
  Probe for shaded jars with parsing Maven poms.
Merge branch 'fix_defaultartifact_hashcode' into bizo

* fix_defaultartifact_hashcode:
  Add m: prefix when reading extra attributes from resolution cache.