it makes no sense to trash the placeholders, and in fact the common
case is that they are deleted due to being replaced by the full
message.
a separate S_PURGED state needed to be added, as S_PURGE needs to be
reset after setting F_DELETED (so the operation doesn't count as still
pending after journal replay), yet trashing needs an indicator. logging
is now done via a separate command, as piggy-backing it on flag updates
just makes things less legible for no benefit.
this is mostly academical, as trashing being done on the side where
placeholders reside is rather unlikely.
this is a lot more legible, and makes it possible to insert values in
the middle without churn.
i didn't find a way to do this with the pre-processor, so we now have
another code generator.
we now use the $< make variable, which requires gmake on netbsd < 9.0,
and possibly other systems with an ancient make.
