catch 409 error

[bourgeoa]

catch 409 error and normalize headers content-type to lower case

[jeff-zucker]

Thanks. I've put this into rest.js so it happens every time a request is received. It handles the general case so headers["Content-Type"] is always treated as headers["content-type"] and options.Method as options.method. The actual methods ('GET','PUT') are upercased but the header keys are lower-cased.

function normalizeOptions(opts){
  let newOpts = {}
  for(var o in opts){
    newOpts[o.toLowerCase()] = opts[o];
  }
  newOpts.method  = newOpts.method ? newOpts.method.toUpperCase() : 'GET'
  return newOpts;
} 

Note : I added your changes manually, so closing this PR without merging.