Partial conversion of registrar to not keep a coro alive for the whole span of the registration.
Convert query_params to a map
Remaining conversion of registrar to not use coroutines, plus coro pool size tuning. (currently still buggy)
Merge pull request #2812 from gsathya/query_params

Convert query_params to a map
Convert header_lines into a map

Also, add a add_header_line() to http_req_t
Fixes bug in disconnect_watcher_t that was triggered if it was the last thing keeping a connection alive.
Improvements in non-coroutine registrar.
removing an extra import form a merge glitch

reviewed over-the-shoulder by danielmewes
adding r.http binary result_format to the server
adding r.http binary result_format polyglot tests
Update content-length only if already present
Use auto for type inference
Add only the first unique value into query_params
Add header only if they're not present
Merge pull request #2818 from gsathya/header_lines

Convert header_lines into a map
Merge branch 'next' into daniel_2211_nocoro_registrar
Merge branch 'next' into sam_2789_keyfix