Add support for the xsiframe linker

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Put this in your gwt.xml file to enable the cross site iframe linker:
<add-linker name="xsiframe"/>

2. Now try to invoke a service
    final SomethingAsync async = (SomethingAsync) SyncProxy.newProxyInstance(SomethingAsync.class, "http://localhost:8181/demo/", "something");

The it fails to locate the RPC policy file because it seems to be searching for 
the .html file instead:
Apr 02, 2014 10:33:30 AM com.gdevelop.gwt.syncrpc.RpcPolicyFinder 
searchPolicyFileInClassPath
WARNING: No RemoteService in the classpath
java.io.FileNotFoundException: 
http://localhost:8181/demo/86EBC63739EDC1C97035068CEB616B35.cache.html
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1623)
    at com.gdevelop.gwt.syncrpc.RpcPolicyFinder.getResposeText(RpcPolicyFinder.java:123)
    at com.gdevelop.gwt.syncrpc.RpcPolicyFinder.fetchSerializationPolicyName(RpcPolicyFinder.java:84)
    at com.gdevelop.gwt.syncrpc.SyncProxy.newProxyInstance(SyncProxy.java:236)
    at com.gdevelop.gwt.syncrpc.SyncProxy.newProxyInstance(SyncProxy.java:219)
    at com.gdevelop.gwt.syncrpc.SyncProxy.newProxyInstance(SyncProxy.java:193)
    at com.gdevelop.gwt.syncrpc.SyncProxy.newProxyInstance(SyncProxy.java:118)
    at com.acme.demo.inttest.GetRawInputTest.test(GetRawInputTest.java:42)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

What version of the product are you using? On what operating system?
GWT 2.6.0 and gwt-syncproxy 0.4.2

Original issue reported on code.google.com by david.nouls on 2 Apr 2014 at 8:35