Replace Exp[_] with Exp[Any] in many places

This is the first batch of such changes I'm testing, it affects most of
the transformation infrastructure.

Rationale: Scalac has poor support for Exp[_]. Exp[Any] is better
because Exp is covariant. We also have functions from Exp[_], but they
are mostly Exp transformers, which are in fact supposed to match on
arbitrary expression nodes.
More Exp[_] ↦ Exp[Any]
Drop workarounds for older Scalac

The problems described here were either fixed in Scalac or by the switch
to Exp[Any]. I'm happy either way.
Merge branch 'master' into topic/better-traversals

Conflicts:
	src/main/scala/ivm/expressiontree/Exp.scala
Drop extra cast
Exp: Import Scalaz, implement __foldMap
Reimplement __findGen2 using foldMap
Fold 'filter' inside __findGen2
Update projects to include library sources

This helps navigation. The change is done by configuring sbteclipse,
regenerating the files, and forcing Eclipse to renormalize them to
remove spurious changes and be able to check the output.

After the changes to build.sbt, the generated project file is much
closer to being usable (save for a bug on scalac options for language
levels).