--disable-shared is entirely broken these days

A gripe today in pgsql-novice made me realize that configure's
--disable-shared option has been useless since 9.0, because it prevents
plpgsql.so from being built, which causes initdb to fail now that
plpgsql is installed "by default" --- which actually seems to mean
"you don't have any choice about whether to install it".

So, a few questions:

1. Should we honor the promise implicit in the "by default" wording
that there should be a way to initdb without plpgsql?

2. Seeing that this is the first complaint since 9.0, should we decide
that --disable-shared is no longer worth supporting? Seems like we
should either make this case work or remove this switch. I notice
that the switch isn't documented anywhere in the SGML docs, either.
If we do keep it, we'd better document that it results in a severely
crippled version of Postgres.

regards, tom lane