Bunyan

- [issue 244] Make `bunyan` defensive on `res.header=null`.

- [issue 233] Make `bunyan` defensive on res.header as a boolean.
- [issue 242] Make `bunyan` defensive on err.stack not being a string.

- Allow `log.child(...)` to work even if the logger is a *sub-class*
of Bunyan's Logger class.
- [issue 219] Hide 'source-map-support' require from browserify.
- [issue 218] Reset `haveNonRawStreams` on `<logger>.addStream`.

- [pull 127] Update to dtrace-provider 0.4.0, which gives io.js 1.x support
for dtrace-y parts of Bunyan.

- [pull 182] Fallback to using the optional 'safe-json-stringify' module
if `JSON.stringify` throws -- possibly with an enumerable property
getter than throws. By Martin Gausby.

- Export `bunyan.RotatingFileStream` which is needed if one wants to
customize it. E.g. see issue 194.

- [pull 122] Source Map support for caller line position for [the "src"
field](https://github.com/trentm/node-bunyansrc). This could be interesting
for [CoffeeScript](http://coffeescript.org/documentation/docs/sourcemap.html)
users of Bunyan. By Manuel Schneider.

- [issue 164] Ensure a top-level `level` given in `bunyan.createLogger`
is *used* for given `streams`. For example, ensure that the following
results in the stream having a DEBUG level:

var log = bunyan.createLogger({
name: 'foo',
level: 'debug',
streams: [
{
path: '/var/tmp/foo.log'
}
]
});

This was broken in the 1.0.1 release. Between that release and 1.3.0
the "/var/tmp/foo.log" stream would be at the INFO level (Bunyan's
default level).