${prefix} variable contains invalid value for .sh startup scripts

Hello!

I have updated my -current system for the first time since Apr 1st,
and postgresql(databases/postgresql81-server) doesn't start here
anymore.

Error message at startup is:
exec: /etc/rc//bin/pg_ctl: not found

postgresql installs /usr/local/etc/rc.d/010.pgsql.sh startup script,
which contains the following line:

command=${prefix}/bin/pg_ctl

I have noticed some messing with ${prefix} in /etc/rc.subr rev. 1.52,
and indeed, reverting to 1.51 caused postgresql to start again.

Who is wrong here? rc.subr? or postgresql startup script shouldn't use
${prefix} variable?

-- 
WBR, Victor V. Snezhko
E-mail: snezhko_at_indorsoft.ru