Need a robust surface mesh repairing tool

[fangq]

Removing self-intersecting elements is extremely important, however, the current available method, meshcheckrepair('meshfix') calls meshfix (https://code.google.com/p/meshfix/) made by Marco Attene et al. which can only repair simple surfaces (homologous to a sphere). We need something more general to deal with complex surfaces such as two intersecting spheres.