1.72 released

1. Mac: Now possible to write a "@" in the contest dialog.
2. New levels (mission01_mod, race10_4pl_mod).
3. Source tree should now build on all 3 platforms.
4. More code comments.
5. Web code added to src.
6. Web replay code added to src.
7. Added zip_exec utility and fixed release build script.
8. Fixed so computer enemies behaves ok if the master leaves.
9. Fixed key repeat issue in map editor.