[core] do not send SIGHUP to process group unless server.max-workers is used (fixes...

[core] do not send SIGHUP to process group unless server.max-workers is used (fixes #2711)

do not propagate sighup if 0 == server.max-workers; reduce impact of
sighup on child processes, such as piped loggers, by not forwarding
sighup signal unless server.max-workers configured

For those configuring server.max-workers, it is recommended that
piped loggers be used to avoid log corruption, and then admins can
avoid sending lighttpd SIGHUP as there is currently no benefit to
doing so with the standard modules (beyond that of log rotation of
non-piped access and error logs).

From: Glenn Strauss <gstrauss@gluelogic.com>

git-svn-id: svn://svn.lighttpd.net/lighttpd/branches/lighttpd-1.4.x@3076 152afb58-edef-0310-8abb-c4023f1b3aa9