gRPC: improved keepalive handling. The code is now able to parse additional control frames after the response is received, and can send control frames as well. This fixes keepalive problems as observed with grpc-c, which can send window update and ping frames after the response, see http://mailman.nginx.org/pipermail/nginx/2018-August/056620.html.

if exists("b:did_indent")
    finish
endif
let b:did_indent = 1

setlocal indentexpr=

" cindent actually works for nginx' simple file structure
setlocal cindent
" Just make sure that the comments are not reset as defs would be.
setlocal cinkeys-=0#