Fix reserved properties

If you do `trace('foo', { name: 'bar' })` that overrides an internally property, but you're not notified of that.

The first commit implements warning on the server's stderr, if you just want to merge that.

However, the client should ultimately print the error, so the client is the only site jstrace ever prints something on.

`server.error(str)` and `remote.error(str)` could probably be combined somehow...