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

@@ -234,6 +234,7 @@ public class MinecraftServer implements Runnable, ICommandListener {
             // 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() + ")");
+            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;

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

@@ -485,6 +485,7 @@ public final class CraftServer implements Server {
         pluginManager.callEvent(new WorldInitEvent(internal.getWorld()));
         System.out.print("Preparing start region for level " + (console.worlds.size() -1) + " (Seed: " + internal.getSeed() + ")");
 
+        if (internal.getWorld().getKeepSpawnInMemory()) {
             short short1 = 196;
             long i = System.currentTimeMillis();
             for (int j = -short1; j <= short1; j += 16) {
@@ -511,6 +512,7 @@ public final class CraftServer implements Server {
                     }
                 }
             }
+        }
         pluginManager.callEvent(new WorldLoadEvent(internal.getWorld()));
         return internal.getWorld();
     }

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

@@ -783,4 +783,26 @@ public class CraftWorld implements World {
     public int getMaxHeight() {
         return 128;
     }
+
+    public boolean getKeepSpawnInMemory() {
+        return world.keepSpawnInMemory;
+    }
+
+    public void setKeepSpawnInMemory(boolean keepLoaded) {
+        world.keepSpawnInMemory = keepLoaded;
+        // Grab the worlds spawn chunk
+        ChunkCoordinates chunkcoordinates = this.world.getSpawn();
+        int chunkCoordX = chunkcoordinates.x >> 4;
+        int chunkCoordZ = chunkcoordinates.z >> 4;
+        //  Cycle through the 25x25 Chunks around it to load/unload the chunks.
+        for (int x = -12; x <= 12; x++) {
+            for (int z = -12; z <= 12; z++) {
+                if (keepLoaded) {
+                    loadChunk(chunkCoordX + x, chunkCoordZ + z);
+                } else {
+                    unloadChunk(chunkCoordX + x, chunkCoordZ + z);
+                }
+            }
+        }
+    }
 }