Started to implement TrPlaneStress2dXFEM, a three node triangle with
XFEM capability.
Added TrPlaneStress2dXFEMClass in classtype.h
Made some functions in XfemElementInterface virtual.
Added possibility to include headers from the Boost library and
continued with xfem implementation. Also implemented piecewise linear
polygon description of cracks and added routines for writing cracks and
cut xfem elements to vtk.
Added debug output for xfem.
Merge branch 'master' of git://github.com/Micket/oofem
Continued xfem implementation for cracks:
 * Heaviside enrichment can now be used with 3-node triangles
(trplanstrssxfem). (No crack tip enrichment available yet).
   NOTE: Boost must be included to simulate cracks.
 * Added small validation case for crack simulation: xFemCrackVal
 * Added combined implicit/explicit crack description with level sets.
 * Added some debug output to vtk for xfem.
Removed StVenantKirchhoff material since the same result can be obtained
by using linear elasticity with geometric nonlinearity.
Added Griffith damage model. Numbered CharType values.
Renamed functions for accessing max and min elements.
Removed StVenantKirchhoffMaterialStatusClass
Removed stvenantkirchhoffortho.C
Merge branch 'master' of git://github.com/Micket/oofem
Corrected syntax in xfem vtkxml debug output.
Added default (iterative) implementations for *Layer and Fiber material modes.
Simplified "computeStrainVectorInLayer" and added direct access functions for different material modes in cross-section.
Added explicit functions for the standard material modes in the structural cross-section instead of having one lots of conditional statements. Material models will then overload the material modes they support (even if they internally use a common function when computing). Such material models should however properly implement the 3D-version in order to support the other material modes that they are missing.
Removed completely unused 3dRotContinuum (should be identical to PlaneStrain either way, or just the 3dMat mode can be used as it makes little difference).
Added convenience function giveStructuralCrossSection() to reduce the amount of visible casts in the code.
Added material status for TwoFluidMaterial model which removes the need for MaterialStatus dictionaries in GPs.