[mc] Make state/snapshot comparison work with SMPI variable privatisation

[mc] Make state/snapshot comparison work with SMPI variable privatisation

Changes :

  * a snapshot region now has a standard address (address in the
    virtual process) and permanent address (address of the
    privatisation region, where the memory is always mapped event when
    another process is active);

  * handle privatised memory regions on snapshot and snapshot restore;

  * compare global vaiable separately for each simulated process;

  * the ID of the simulated must be passed everywhere;

  * mc_snapshot_read() and friends as well as DWARF expression can be
    evaluated in the context of a given simulated process and fetch
    the data in the corresponding privatisation region.