Expand three special node types

Can't Enter node renamed to Prevent Action, as it's a more accurate description of what it does. It has been expanded to cover the following cases, all of which are documented:
- When the special node was called during an attack action (which involves a weapon whose ability is to call a special node when attacking, or an item or monster ability that calls a special node when hit), then Prevent Action reverses the action point cost.
- When called as the result of a purchase (a shop item that calls a special), then Prevent Action prevents gold from being deducted (which is also new in this commit, as before it never deducted gold)
- When called as the result of using a normal item (not a special item), then Prevent Action prevents a charge from being deducted
- When called as the result of a monster using its ability, then Prevent Action prevents the action points from being deducted
- Cases it already covered (cancelling initiation of talk mode, searching of containers, outdoor wandering encounters) have been documented
- The fact that it will break things during talk mode is also documented now

Start Spell Targeting node has been tweaked and gained some new options:
- You can allow the player to target opaque or antimagic spaces. In town mode, you can prohibit them from targeting antimagic spaces.
- You can specify a special node to be called if targeting fails because they selected an invalid space, or because an special node keyed to spellcasting context cancelled it
- You no longer get a "Hit 'p' to cancel" message. Even better, hitting 'p' does not cancel it. (Well, more precisely, it triggers the failure node, with the party's or pc's location as the target space.)

Misc:
- Fix crash outdoors due to trying to check for force barriers

rsrc/strings/specials-text-general.txt

@@ -174,7 +174,7 @@ Unused
 Unused
 Special to Jump To
 --------------------
-Can't Enter
+Prevent Action
 Unused
 Unused
 First part of message
@@ -182,7 +182,7 @@ Second part of message
 Unused
 Unused
 Unused
-0 - can enter, 1 - no enter
+0 - allow, 1 - prevent
 Unused
 Unused
 0 - don't force, 1 - force if blocked

rsrc/strings/specials-text-town.txt

@@ -489,9 +489,9 @@ Unused
 Which spell pattern? (0 - single space)
 Max range? (ignored outside combat mode)
 Max targets? (>1 only in combat)
-Unused
-Unused
-Unused
+Special Called if Targeting Fails
+if 1, allow obstructed spaces
+if 1, allow targeting in antimagic fields
 Special to Call for Each Target
 --------------------
 Place Fields in Spell Pattern