of the observer pattern
next Commit of NavierStokesWithFlux will show how to use
the observer pattern

Some pollution: I need these overloading to commit a first release of DG-FEM test, but they will be cancelled out when the new version of pattern (or whatever it will be) is ready (see C. Winkelmann's mail on life-dev mailing list).

It is used to retrieve the exact type of a class
when using class hierarchies

* added Cloning factory aka abstract factory
  it will be used in the boundary conditions classes
* testsuite/lifecore/test_factory.cpp has a test for clone factories
  now
* test_factory is now enabled

this is the first COMMIT that makes boost:: a requirement !

factories rely on boost::function<> for functors.

dependencies are not ok

two tests are performed : 1 for tetra, 1 for hexa meshes.

BEWARE : data files are modified!!
In particular they must contain the entry
[darcy/discretization]
mesh_faces   = all      # OBLIGATORY! we need all faces!

to construct the face-volume lists.
(new "feature" linked to the use of DataMesh)

I will commit a new version of assemb.hpp which should be explanatory
of usefulness and usage.

and the sparsity pattern independent. see also file REDESIGN.txt and
discussion on lifev-dev@webmail.mate.polimi.it

bcHandler.hpp should be used instead of bcCond.hpp
moved bcFunction into its own files like bcVector

* renamed variables according to coding standard
* trigger error calculation from outside

* do not calculate errors any more, user may use new error functions
  from NavierStokesHandler instead
* do not set any artificial pressure boundary condition for matrix definiteness

* get time from argument list instead of (inexistent) member in error functions

be careful boost will become mandatory RSN !

of mean values useful for fields defined up to a constant