CAVE_ICKY -> CAVE_VAULT
Start undoing the view_g/view_n hack.

This array is used as a list of viewable cells in the dungeon at every update
step.
pessimize update_view
Stop using CAVE_TEMP in spells2.c
CAVE_TEMP -> CAVE_WASSEEN
Kill temp_g.
Destroy view_g and view_n.
Kill off fast_cave_info.
Split out add_monster_lights().
Factor out view-updating code from the heinous loop in update_view().
Refactor cave_illuminate() to be less ugly.
Have update_view and forget_view take a cave to operate on.
Destroy vinfo_hack altogether
And remove vinfo for good.
Only allow sight out to MAX_SIGHT.
Tasteful wall-visibility hack.
Don't steal los through double-thick walls.
Detect and work around the 'knight's move' LOS hack when doing FOV.

We shouldn't steal LOS from an adjacent square if that square was reached with
the knight's move hack.
Convert more cave->feat accesses to functions.
Reduce drop frequency for town books as monster drops
(cherry picked from commit 2fe64775ed7ae0a40358e1475f31719756e8ba0c)