jnr.ffi.VarargsTest#testSizeT failes on Windows

[goto1134]

Before I appyed #135, vararg class tests failed with UnsatisfiedLinkError on Windows OS.
After the fix I found out the other problem. The testSizeT test fails with the following message (number of line changed because of the fix):

java.lang.AssertionError: 
Expected :5
Actual   :2

	at org.junit.Assert.fail(Assert.java:88)
	at org.junit.Assert.failNotEquals(Assert.java:743)
	at org.junit.Assert.assertEquals(Assert.java:118)
	at org.junit.Assert.assertEquals(Assert.java:555)
	at org.junit.Assert.assertEquals(Assert.java:542)
	at jnr.ffi.VarargsTest.testSizeT(VarargsTest.java:41)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	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$2.evaluate(ParentRunner.java:229)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

jnr-ffi/src/test/java/jnr/ffi/VarargsTest.java

Lines 34 to 40 in 4697272

	@Test public void testSizeT() {
	Pointer ptr = Runtime.getRuntime(c).getMemoryManager().allocate(5000);
	int size = c.snprintf(ptr, 5000, "%zu", size_t.class, 12345);
	Assert.assertEquals(5, size);
	String result = ptr.getString(0, size, Charset.defaultCharset());
	Assert.assertEquals("12345", result);
	}

After debugging I found out that the result string is "zu" instead of "12345".

[zhanhb]

Here should be %Iu on windows.
https://msdn.microsoft.com/en-us/library/tcxf1dw6.aspx