Fix #597

NaN and Infinity were replaced in the output generation, instead of
during compression. This could lead to results where `1/0` was inserted
without parens leading to invalid output.

The nodes are replaced in the compression step now, and the output
generation returns their regular names. This should not be a problem,
since they're already only constructed from the original name.

test/compress/issue-597.js

@@ -0,0 +1,25 @@
+NaN_and_Infinity_must_have_parens: {
+    options = {};
+    input: {
+        Infinity.toString();
+        NaN.toString();
+    }
+    expect: {
+        (1/0).toString();
+        (0/0).toString();
+    }
+}
+
+NaN_and_Infinity_should_not_be_replaced_when_they_are_redefined: {
+    options = {};
+    input: {
+        var Infinity, NaN;
+        Infinity.toString();
+        NaN.toString();
+    }
+    expect: {
+        var Infinity, NaN;
+        Infinity.toString();
+        NaN.toString();
+    }
+}