[JENKINS-25118] Allow signatures with primitives

[ikedam]

JENKINS-25118

As Class#isinstance(Object) always returns false for primitives, the sandbox fails to identify methods with primitive arguments.
http://docs.oracle.com/javase/6/docs/api/java/lang/Class.html#isInstance%28java.lang.Object%29

This change allows the sandbox work for methods with primitive arguments.

[ikedam]

test #71 demonstrates reproduction of this problem (committed a test with no fix).

java.lang.AssertionError: org.jenkinsci.plugins.scriptsecurity.sandbox.RejectedAccessException: unclassified method java.lang.String charAt java.lang.Integer
    at org.junit.Assert.fail(Assert.java:88)
    at org.junit.Assert.assertTrue(Assert.java:41)
    at org.junit.Assert.assertNotNull(Assert.java:621)
    at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptorTest.primitiveTypes(SandboxInterceptorTest.java:339)

[jenkinsadmin]

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