#33 Adopt XDoclet's notion of "substitutions"

[Dave Neuer]

Deprecate interface package in favor of XDoclet's
notion of package substituions.

Not doing this causes problems, say, when Middlegen
puts valueobjects into "interfacePackage" but in their
EJBDoclet valueobject subtask, the user specifies a
substitution like <packageSubstitution packages="ejb"
substituteWith="model"/> .

The equivalent (I think) of a top level
<packageSubstitution packages="whatever"
substituteWith="interfaces"/> can be had w/ something
like "*:whatever=interfaces."

This requires the user to call plugin.getSubstitutio()
explicitly for the object type they're interested in.

Logic could be added to support "*:*=interfaces" too,
to mimic <packageSubstitution
substituteWith="interfaces"/>.

[Dave Neuer]