Generate safe sourcemaps

The previous comment syntax was unsafe with Internet Explorer. This
change copies the equivalent upstream change to use the more robust
nested comment:

```javascript
/*
//@ sourceMappingURL=file.min.js.map
*/
```

See:
    https://github.com/mishoo/UglifyJS2/issues/108
    http://bugs.jquery.com/ticket/13274
Update test fixtures
Merge pull request #44 from acdha/safe-sourcemaps

Generate safe sourcemaps
Disable sorting of names before mangling to provide stable name mangling and to decrease file size after gzipping. fixes #37, see also https://github.com/mishoo/UglifyJS2#mangler-options
Update fixtures for stable name mangling.
Bumped uglify-js to v2.3.0 (Fixes #40)
Updated to uglify-js v2.3.5
Fixed typo in multiple_sourcemaps2.map fixture
Updated to new sourceMappingURL syntax

The upstream specification has changed from //@ to //# which avoids IE
conditional comment compatibility issues and thus the need to wrap the
declaration in a /* */ comment.

See:
    https://github.com/mishoo/UglifyJS2/pull/213#issuecomment-18215308
    https://bugzilla.mozilla.org/show_bug.cgi?id=870361
Merge branch 'safe-sourcemaps' of git://github.com/acdha/grunt-contrib-uglify into acdha-safe-sourcemaps

* 'safe-sourcemaps' of git://github.com/acdha/grunt-contrib-uglify:
  Updated to new sourceMappingURL syntax
Merge branch 'master' of git://github.com/regru/grunt-contrib-uglify into regru-master

* 'master' of git://github.com/regru/grunt-contrib-uglify:
  Update fixtures for stable name mangling.
  Disable sorting of names before mangling to provide stable name mangling and to decrease file size after gzipping. fixes #37, see also https://github.com/mishoo/UglifyJS2#mangler-options
updated documentation, changelog
0.2.1
Add support for enclose option.