Throw exception if headers are set through curl options.
Throw exception if headers are set through curl options.

Fixes #1886

robertlemke/flow-development-collection,kdambekalns/flow-development-collection,fcool/flow-development-collection,daniellienert/flow-development-collection,fcool/flow-development-collection,daniellienert/flow-development-collection,kdambekalns/flow-development-collection,robertlemke/flow-development-collection,robertlemke/flow-development-collection,fcool/flow-development-collection,neos/flow-development-collection,fcool/flow-development-collection,kdambekalns/flow-development-collection,kdambekalns/flow-development-collection,neos/flow-development-collection,neos/flow-development-collection,robertlemke/flow-development-collection,daniellienert/flow-development-collection,neos/flow-development-collection