implement object rest/spread (#2265)

- improve parse errors for destructuring spread elements
- `unsafe` for object literals with rest elements

Miscellaneous
- increase mocha unicode surrogate test timeout

lib/compress.js

@@ -1731,6 +1731,7 @@ merge(Compressor.prototype, {
                 var val = {};
                 for (var i = 0, len = this.properties.length; i < len; i++) {
                     var prop = this.properties[i];
+                    if (prop instanceof AST_Expansion) return this;
                     var key = prop.key;
                     if (key instanceof AST_Symbol) {
                         key = key.name;