start in on fixpoint redesign
add applySpre, applySpost; fix some type errors; comment out some code
fix 'envelope'
fix trace
fix typo
make QDiagram back into a newtype (checkpoint)

Doesn't compile, a few more things need to be updated.
See the wiki page for justification: http://www.haskell.org/haskellwiki/Diagrams/Dev/Fixpoint#Diagrams.Core.Types
Merge branch 'fixpoint' into gsoc

Conflicts:
	src/Diagrams/Core/Types.hs
Add path-based traversal into a tree
Make Data.Set.Lens import non-qualified