[ES6] Implemented parse for export Name from Module variants. (#1701)

- add `AST_Export` new variants output
- add tests to `test/compress/`
- update `$propdoc` of `AST_Export` ("exported_names" & "module_name")
- add tests for `export ...  as ...` variants

test/mocha/export.js

@@ -0,0 +1,40 @@
+var assert = require("assert");
+var uglify = require("../../");
+
+describe("Export", function() {
+    it ("Should parse export directives", function() {
+
+        var inputs = [
+            ['export * from "a.js"', ['*'], "a.js"],
+            ['export {A} from "a.js"', ['A'], "a.js"],
+            ['export {A as X} from "a.js"', ['X'], "a.js"],
+            ['export {A as Foo, B} from "a.js"', ['Foo', 'B'], "a.js"],
+            ['export {A, B} from "a.js"', ['A', 'B'], "a.js"],
+        ];
+
+        var test = function(code) {
+            return uglify.parse(code, {fromString: true});
+        };
+
+        var extractNames = function(symbols) {
+            var ret = [];
+            for (var i = 0; i < symbols.length; i++) {
+                ret.push(symbols[i].name.name)
+            }
+            return ret;
+        };
+
+        for (var i = 0; i < inputs.length; i++) {
+            var ast = test(inputs[i][0]);
+            var names = inputs[i][1];
+            var filename = inputs[i][2];
+            assert(ast instanceof uglify.AST_Toplevel);
+            assert.equal(ast.body.length, 1);
+            var st = ast.body[0];
+            assert(st instanceof uglify.AST_Export);
+            var actualNames = extractNames(st.exported_names);
+            assert.deepEqual(actualNames, names);
+            assert.equal(st.module_name.value, filename)
+        }
+    })
+});