Don't overwrite a bundle file if the hash is the same about catberry

[rdner]

It does not seem enough useful for me to implement this feature.

If you have a big app and automated deployment it does not matter if the file is overwritten or not. It's expected from Catberry users (developers) that they put externals.js somewhere on CDN and take care of versioning of this script when needed as a build step for their CI/CD.

The only way to implement this feature is to have a temporary file which browserify is streaming the bundle into and then compute the hash of the file and compare it to the existing file's hash. We could do that but browserify is already streaming to a temporary file and we would introduce another one because we can not integrate anything in the browserify process.

So, the solution would be very inefficient and would slow down the build process because of the hash computing.