Add vision sanity checking, fix more vision

- Add a vision sanity checking routine

- Recalc block point when digging a door for temporary clouds

- Add recalc_block_point after cvt_sdoor_to_door, because doorways
  on the Rogue level have no doors, and otherwise the sanity checking
  would complain.  This doesn't actually change how the Rogue level
  vision works, as it uses a different vision system

- Monster using a trap in a secret corridor revealed the corridor,
  but didn't unblock the vision unless you saw the location

include/extern.h

@@ -3502,6 +3502,7 @@ extern int assign_videocolors(char *) NONNULLARG1;
 
 /* ### vision.c ### */
 
+extern boolean get_viz_clear(int, int);
 extern void vision_init(void);
 extern int does_block(int, int, struct rm *) NONNULLARG3;
 extern void vision_reset(void);