Updated maven shade plugin to version 2.1

The currently used maven shade plugin still keeps references to the
original classes in their constant pools around. This is never a problem
at runtime, but for dependency tools which try to use the constant pool
for determining dependencies will get confused (OSGI for example). This
patch simply bumps the version and will implicetely fix
fix http://jira.codehaus.org/browse/MSHADE-105

Closes #3254
Closes #3255