Extracted dense assembly to a separate helper class.
Small formatting change.
Added getGlobalDofBoundingBoxes() and getFlatLocalDofBoundingBoxes() to Space.
Made return type of constructOperatorMapping...() more specific.
IndexPermutation::permutedIndices() avoids copying a vector.
Added IndexPermutation::permutationMatrix().
AhmedLeafClusterArray now allows write access to its elements.
Added _3dArray::is_empty().
Extensive changes in clustering and admissibility conditions.

1. We now use bounding boxes instead of bounding spheres.
2. The "disassembled mode" now works differently than before. Previously
   it assembled H-matrices indexed with local degrees of freedom, which
   were then sandwiched between sparse matrices mapping global to local
   dofs and v.v. The three matrices were stored separately. This is still
   what happens in the assembly of "synthetic operators". Now we assemble
   H-matrix blocks indexed with local dofs, but once a given block is
   calculated, it is immediately multiplied by the relevant blocks of the
   gdof<->ldof mapping matrices, and stored in a form indexed with gdofs.
   This makes it possible to reduce peak memory usage.
Added the HypersingularIntegralOperator class.

It can be used to define an operator whose weak form is calculated
differently in admissible and nonadmissible blocks.
Added a new implementation of the Laplace hypersingular operator.
Corrected AHMED patches, circumventing a problem with python_patch.
Prevented Space::get*BoundingBoxes() from being wrapped in the Python bindings.
Dispensed with some unnecessary virtual function calls in RaviartThomas0VectorSpace.
Added rudimentary implementation of get*BoundingBoxes() to RaviartThomas0VectorSpace.
Merge branch 'coalesced_operators' of https://github.com/bempp/bempp into coalesced_operators
Edited docs of laplace3d[Synthetic]HypersingularBoundaryOperator().
Implemented new-style "disassembled" hypersingular op. for Helmholtz eq.
Slightly accelerated calculation of some complex integrals
(by performing as many arithmetic operations as possible with real numbers).
Added missing includes, thereby fixing a memory leak in destructor of
auto_ptr to instance of incomplete class.