It defines a variable and its default value in load_rc_config() just after
rc.conf is loaded. "rcvar" command shows the current and the default values.
This is an attempt to solve a problem that rc.d scripts from third-party
software do not have entries in /etc/defaults/rc.conf. The fact that
load_rc_config() reads rc.conf only once and /etc/rc invokes the function
before running rc.d scripts made developers confused for a long time because
load_rc_config() just before run_rc_command() in each rc.d script overrides
variables only when the script is directly invoked, not from /etc/rc.
Variables defined in set_rcvar are always set in load_rc_config() after
loading rc.conf. An rc.d script can now be written in a self-contained
manner regarding the related variables as follows:
---
name=foo
rcvar=foo_enable
set_rcvar foo_enable YES "Enable $name"
set_rcvar foo_flags "-s" "Flags to $name"
...
load_rc_config $name
run_rc_command "$@"
---
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