Fix bug in caching of vset_next in LDD.
- Initialize domain of sets and rel with read and/or write projection.
 - Create relation according to read and write projection.
 - Fix mdd_next to use read and write projections.
 - Fix rel_add_mdd to support read write nodes.
 - Change other function to use the combined read/write projection.
 - Add logical or operation on two dependency matrices
 - Fix dependency matrix operations not to let a 'w' dependency subsume a '-' dependency.
 - Fix GB functions to use the read and write projections.
 - Now also print stats of group_explored.
fix zip version (>= 10), so we can compile ltsmin on Arch Linux.