output optimal representations of NaN & Infinity (#1723)

- move these optimisations out from `Compressor` to `OutputStream`
- fixes behaviour inconsistency when running uglified code from global or module levels due to redefinition

test/compress/issue-597.js

@@ -6,7 +6,7 @@ NaN_and_Infinity_must_have_parens: {
     }
     expect: {
         (1/0).toString();
-        NaN.toString();         // transformation to 0/0 dropped
+        (0/0).toString();
     }
 }
 
@@ -23,3 +23,87 @@ NaN_and_Infinity_should_not_be_replaced_when_they_are_redefined: {
         NaN.toString();
     }
 }
+
+beautify_off_1: {
+    options = {
+        evaluate: true,
+    }
+    beautify = {
+        beautify: false,
+    }
+    input: {
+        var NaN;
+        console.log(
+            null,
+            undefined,
+            Infinity,
+            NaN,
+            Infinity * undefined,
+            Infinity.toString(),
+            NaN.toString(),
+            (Infinity * undefined).toString()
+        );
+    }
+    expect_exact: "var NaN;console.log(null,void 0,1/0,NaN,0/0,(1/0).toString(),NaN.toString(),(0/0).toString());"
+    expect_stdout: true
+}
+
+beautify_off_2: {
+    options = {
+        evaluate: true,
+    }
+    beautify = {
+        beautify: false,
+    }
+    input: {
+        console.log(
+            null.toString(),
+            undefined.toString()
+        );
+    }
+    expect_exact: "console.log(null.toString(),(void 0).toString());"
+}
+
+beautify_on_1: {
+    options = {
+        evaluate: true,
+    }
+    beautify = {
+        beautify: true,
+    }
+    input: {
+        var NaN;
+        console.log(
+            null,
+            undefined,
+            Infinity,
+            NaN,
+            Infinity * undefined,
+            Infinity.toString(),
+            NaN.toString(),
+            (Infinity * undefined).toString()
+        );
+    }
+    expect_exact: [
+        "var NaN;",
+        "",
+        "console.log(null, void 0, 1 / 0, NaN, 0 / 0, (1 / 0).toString(), NaN.toString(), (0 / 0).toString());",
+    ]
+    expect_stdout: true
+}
+
+beautify_on_2: {
+    options = {
+        evaluate: true,
+    }
+    beautify = {
+        beautify: true,
+    }
+    input: {
+        console.log(
+            null.toString(),
+            undefined.toString()
+        );
+    }
+    expect_exact: "console.log(null.toString(), (void 0).toString());"
+}