Implement PortalCreateEvent reason codes. Addresses BUKKIT-833

This commit modifies the construction of PortalCreateEvents to specify
a reason for the event.  Reasons are either:
1. FIRE: the portal is being created because a player set fire to an
obsidian frame.
2. DESTINATION: the portal is being created as a destination for an existing portal.

src/main/java/net/minecraft/server/BlockPortal.java

@@ -95,7 +95,7 @@ public class BlockPortal extends BlockHalfTransparant {
                 }
             }
 
-            PortalCreateEvent event = new PortalCreateEvent(blocks, bworld);
+            PortalCreateEvent event = new PortalCreateEvent(blocks, bworld, PortalCreateEvent.CreateReason.FIRE);
             world.getServer().getPluginManager().callEvent(event);
 
             if (event.isCancelled()) {

src/main/java/org/bukkit/craftbukkit/PortalTravelAgent.java

@@ -341,7 +341,7 @@ public class PortalTravelAgent implements TravelAgent {
             }
         }
 
-        PortalCreateEvent event = new PortalCreateEvent(blocks, (org.bukkit.World) craftWorld);
+        PortalCreateEvent event = new PortalCreateEvent(blocks, (org.bukkit.World) craftWorld, PortalCreateEvent.CreateReason.OBC_DESTINATION);
         Bukkit.getServer().getPluginManager().callEvent(event);
         if (event.isCancelled()) {
             return false;