Consider including directory name into the stack trace for some files

[gaearon]

See https://twitter.com/deadcoder0904/status/929050109425229824

Maybe if the file is called index.js (pretty common with some directory structures) we should include the directory name into the short component stack trace.

[gaearon]

Not sure how well that would work but I'd love to see an example. You'll need to change describeComponentFrame() if I recall correctly.

[xjlim]

@gaearon I'd like to work on this.

[gaearon]

Sounds good, it's yours!