[core] adaptive spawning for socket backend procs (fixes #1162)
[core] adaptive spawning for socket backend procs (fixes #1162)

*experimental*

enable adaptive spawning for socket backend processes

new feature will allow "min-procs" => "0" and will spawn a backend
upon receipt of a request, if no backends are currently running.
This may be useful on resource-limited systems where there is a
seldom-used resource-intensive backend, such as home router
configuration web pages.  The first request may be slower as the
backend is starting up, but then subsequent requests within
"idle-timeout" will hit the (temporarily) persistent backend for
faster responses.

x-ref:
  "Adaptive spawning with min-procs=>0"
  https://redmine.lighttpd.net/issues/1162

gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4