SemanticSubstitute sensitive to internal replacements map ordering

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The test below (com.sri.ai.test.grinder.GrinderTest.testSubstitute()) is 
sensitive to the map's internal ordering, and it should not be.

The current map order generates output "10 + 10", but if stored in a different 
order we get "2 + 10".

        expression   = parse("x + 2");
        replacements = Util.map(
                parse("x"), parse("2"),
                parse("2"), parse("10"));
        expected     = parse("10 + 10");
        testSemanticSubstitute(replacements, process);

This was noticed when the underlying map was changed from HashMap to 
LinkedHashMap

Changing the semantic substitute to an exhaustive replacement does not work as 
it may cause infinite recursion.

Original issue reported on code.google.com by [email protected] on 11 Feb 2014 at 8:15