Make OPENSSL_config truly ignore errors.

Per discussion: should not exit. Should not print to stderr.
Errors are ignored.  Updated doc to reflect that, and the fact
that this function is to be avoided.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>