Use of tpnme.EMPTY and nme.EMPTY instead of new common vals.

Instead of creating new a TypeName and a TermName to change
all the types in the tree to add reduncancy (since the types will
be stored separately), we used the default empty types.
Merge branch 'master' of https://github.com/aghosn/persistence

Conflicts:
	plugin/src/main/scala/scala/reflect/persistence/Plugin.scala