Do not modify Error or Date objects when logging. Fixes #610

[harriha]

Hi,

Ended up taking a stab on this issue, but not 100% sure if this is the best way to do it (and is this all) since I'm not that familiar with this lib - review welcome, luckily there's not much changes.

My concerns/notes:

• I'm on Windows, where a bunch of tests fails locally, but I'm sure travis will tell if things are ok or not
• Are there perf concerns here in some envs since now creating new Error/Date objects - probably not a real issue
• Are tests in logical places and as good as they can be (not familiar with vows previously either)

The fact that these types of objects were returned as-is from clone() in the first place puzzles me a bit, wonder if there was something non-obvious behind that approach.

In case there's something to fix, please let me know.

[indexzero]

Thank you for your contribution. The inner working of clone is going to change significantly in winston@3.0.0, but this may land in the 2.x branch.

[indexzero]

No, this is not going to cut it for winston, sorry. Do this:

copy = new Error(obj.message);
Object.getOwnPropertyNames(obj).forEach(function (key) {
  copy[key] = obj[key];
}); 

return copy;

[indexzero]

@harriha had some cycles (no pun intended) to review the Error clone approach in detail. If you can use Object.getOwnPropertyNames then I think this is good to merge.

This is the last PR I'd like to land before releasing winston@2.0.0 so it will land in the winston@1.x tree.

[indexzero]

Cherry-picked this and made the change myself. Thank you for your contribution!

[harriha]

Hey, great to see this moving forward, thanks! And sorry for that one gotcha, didn't manage to react before you got it done, thanks for pushing this forward - and looking forward for the 2.x release!