Pass a busyobj * to the VCL methods
move VCL::handling from req to wrk
Move cur_method from req to wrk
Follow up on discussion some weeks back, and rename vcl_fetch{}
to vcl_backend_fetch{}, and vcl_response{} to vcl_backend_response{}.
Add a VCL_Ref{} function, we will need to give the fetcher
threads a copy of the VCL.

Reduce move the meat of the inline VCL method functions to
a real function, before things get more complicated.
Add even more arguments to the VCL method functions
Use the busyobj workspace for random VCL work in vcl_backend_*{}

Minor polish
Add a band-aid for now, and pass the bo with the req where bereq/beresp
are available.
Start moving the backend VCL variables to use busyobj rather than req
Set the waiter pipe as non-blocking and record overflows

Fixes #1285
Move be*.status to use busyobj
Move the beresp.do_* variables to busyobj
Move the backend timeout vars to busyobj
Move beresp.storage to busyobj
Rearrange the ttl/grace/keep VRT functions
Move beresp.ttl/grace/keep to busyobj
Move the beresp.backend.* variables to busyobj
Fix indentation in emitted C code
Use the argument provided workspace, rather than default to req->ws.