from this state. 

To that end, a Preprocessing class was added to Import.*.

To save state, the user just has to add the keyword "save" in the info.dat file,
followed by the frequency of save. An archive (containing two binary files
containing displacement and level-set field) is generated at each required step
(save_step_[nbstep].tar).

To do a restart, the user must instantiate and object of the PreProcessing
class, and then call the restartFromFile function, AFTER the constructor of
Algorithm. The name of the restart file can be parsed using ParseRestartFileName
(it still has to be improved).

Then when excecuting the program, the user needs to give the main data file, and 
the name of the restart file, for exemple :

>> ./executable data/main.dat save_step_0010.tar

Normally it should work.

In Export.*, a new exportOnSpace function has been added, to save field when
needed (it can save both scalar field like level-set of vector field like
displacement).

The level-set field is saved in TLSSolver, after reinitiating the level-set
field.

In Formulation.* a saveStep function has been added to save displacement, and
the create an archive file.

In Util.* some functions have been added (toString to convert char* into string,
and fexists to test file existence).



git-svn-id: https://svn.ec-nantes.fr/eXlibris/Applis/TLSDuctile@2136 fbbead7c-fb4d-4173-aa67-51132c73c120