Fix a few "bad example" problems in the rc.d scripts that have been
propogated by copy and paste.
1. Primarily the "empty variable" default assignment, which is mostly
${name}_flags="", but fix a few others as well.
2. Where they are not already documented, add the existence of the _flags
(or other deleted empties) option to the comments, and in some cases add
comments from scratch.
3. Replace things that look like:
prefix=%%PREFIX%%
command=${prefix}/sbin/foo
to just use %%PREFIX%%. In many cases the $prefix variable is only used
once, and in some cases it is not used at all.
4. In a few cases remove ${name}_flags from command_args
5. Remove a long-stale comment about putting the port's rc.d script in
/etc/rc.d (which is no longer necessary).
No PORTREVISION bumps because all of these changes are noops.
