Bug#369351: Bandaid patch

[Florian Weimer]

* Martin Pitt:

> My advice would be to use the autoconf magic and #defines and use
> -Conn() if it's available, and just PQescapeString() if not.
> Otherwise, if you are sure that exim only ever uses one connection at
> a time, then PQescapeString() is completely safe, too.

It's not, no matter what Exim does.  Exim uses NSS, and there is an
NSS module for PostgreSQL which could clobber the internal global
variable.