Destroy Walls at entrances

Added a new function to rooms that is called by players entering an
area. It destroys walls in a small radius around the player, eliminating
the 'trick' aspect of wall spells.

This setup allows walls to be used on exits to block escapes, but does
not allow walls to block entrances. Walls will still function normally
anywhere else in the area, and can still block small passages and the
like, but players will no longer 'stumble' into them.
Added checks

There are some rare but relevant situations where players could still be
using walls to block escape by an enemy. These checks will prevent
destruction of walls by entering angeleds, unguildeds, or DMs.
Renaming, commenting, adjustment

Logon time check in NewOwner replaced with 'if old <> $'. Players
logging on don't have an old owner. The NewOwner function already had
the old owner check and related code.

viWALL_DESTROY_RADIUS is now a room constant. Function is now called
DeleteWallsAroundPlayer, and uses SquaredDistanceTo.
Comments & Battler

Changed the function to DeleteWallsAroundBattler. Given that it works
for monsters, too, it could definitely be used by content creators to
make monsters that inherently clear walls. Really, the applications are
up to whoever calls the function. I just happen to also put in a call
that occurs every time a player enters an area. I updated the comments
to reflect that.
Brambles check & squared

Added check for Brambles & Squared the delete radius to match
measurements
Merge pull request #106 from M59Gar/wallzone

Wall spells destroyed at entrances