Implement "return(retry)" in vcl_backend_error{}
Remove user-guides/cookies.rst from here as well
Remove more nonexistent rst files to please make dist and jenkins
Add a V1D_Deliver_Synth() for delivering synth vcl_error{} responses.
Change vcl_error{} to do a direct response without going the detour
over a bogo-object.

This means that vcl_error{} looses access to obj.* variables, but
gains access to resp.* vaiables instead.

A couple of now obsolute test-cases retired.
Use `Symbol' instead of `Object'

This matches the rest of the code.
Sync with reality

Only varnishreplay is left now.
Update list of rst files
Correctly account the length of vcl_backend_error{} synthetic body.
Unhook varnishreplay for the time being

This will be revisited post 4.0. Reorder while I'm here.