Implemented per world setting to keep the spawn in memory or not.

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

@@ -49,7 +49,7 @@ public class ChunkProviderServer implements IChunkProvider {
         int l = j * 16 + 8 - chunkcoordinates.z;
         short short1 = 128;
 
-        if (k < -short1 || k > short1 || l < -short1 || l > short1) {
+        if (k < -short1 || k > short1 || l < -short1 || l > short1 || !(this.world.keepSpawnInMemory)) { // CraftBukkit - added 'this.world.keepSpawnInMemory'
             this.unloadQueue.add(i, j); // CraftBukkit
         }
     }

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

@@ -232,8 +232,9 @@ public class MinecraftServer implements Runnable, ICommandListener {
         // CraftBukkit start
         for (int l = 0; l < this.worlds.size(); ++l) {
             // if (l == 0 || this.propertyManager.getBoolean("allow-nether", true)) {
-                WorldServer worldserver = this.worlds.get(l);
-                log.info("Preparing start region for level " + l + " (Seed: " + worldserver.getSeed() + ")");
+            WorldServer worldserver = this.worlds.get(l);
+            log.info("Preparing start region for level " + l + " (Seed: " + worldserver.getSeed() + ")");
+            if (worldserver.getWorld().getKeepSpawnInMemory()) {
                 // CraftBukkit end
                 ChunkCoordinates chunkcoordinates = worldserver.getSpawn();
 
@@ -260,7 +261,7 @@ public class MinecraftServer implements Runnable, ICommandListener {
                         }
                     }
                 }
-            // } // CraftBukkit
+            } // CraftBukkit
         }
 
         // CraftBukkit start

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

@@ -83,6 +83,7 @@ public class World implements IBlockAccess {
     // CraftBukkit start
     private final CraftWorld world;
     public boolean pvpMode;
+    public boolean keepSpawnInMemory = true;
     public ChunkGenerator generator;
     Chunk lastChunkAccessed;
     int lastXAccessed = Integer.MIN_VALUE;