Remove inthack and fix i-lock star display

[sim642]

For a long while now, the i-lock star (denoting symbolic index-based locking) hasn't been nicely printed. For example, the warning for the website example shows def_exc:-19012009 as the index:

[Warning][Race] Memory location data[?]@tests/regression/05-lval_ls/18-website.c:4:5-4:13 (race with conf. 110):
  write with [symblock:{i-lock:mutexes[def_exc:-19012009]}, mhp:{tid=[main, t_fun@tests/regression/05-lval_ls/18-website.c:25:3-25:40]}, lock:{mutexes[def_exc:3]}, thread:[main, t_fun@tests/regression/05-lval_ls/18-website.c:25:3-25:40]] (conf. 110)  (exp: & data[i]) (tests/regression/05-lval_ls/18-website.c:9:3-9:12)

After this PR, this is fixed to display the indented and more user-friendly * in its place, as it was originally intended:

[Warning][Race] Memory location data[?]@tests/regression/05-lval_ls/18-website.c:4:5-4:13 (race with conf. 110):
  write with [symblock:{i-lock:mutexes[*]}, mhp:{tid=[main, t_fun@tests/regression/05-lval_ls/18-website.c:25:3-25:40]}, lock:{mutexes[def_exc:3]}, thread:[main, t_fun@tests/regression/05-lval_ls/18-website.c:25:3-25:40]] (conf. 110)  (exp: & data[i]) (tests/regression/05-lval_ls/18-website.c:9:3-9:12)

This removes the global inthack altogether and changes the Printable used for those i-lock accesses to use a custom implementation that explicitly only has unknown and star indices in offsets. During the expression transformation, star is no longer an integer constant with inthack value, but rather has a special varinfo, which only exists in expressions very locally in the symb_locks analysis.

[sim642]

In particular, this would be quite good for the PRIDE presentation or website update if the same example is to be used for screenshots.

[jerhard]

As the documentation of the SymbLocks analysis is currently pretty sparse, it might also make sense to reference the paper in the code.