Added synchronization to Proxy.dispose(). shannah#24

Author: shannah

src/main/java/ca/weblite/objc/Proxy.java

@@ -184,9 +184,11 @@ public static Proxy load(Pointer peer){
      * leave the Objective-C object intact.
      */
     public void dispose(boolean sendDeallocMessage){
-        proxyCache.remove(getPeer());
-        if ( sendDeallocMessage ){
-            send("dealloc");
+        synchronized(proxyCache) {
+            proxyCache.remove(getPeer());
+            if ( sendDeallocMessage ){
+                send("dealloc");
+            }
         }
     }