Core: improved ngx_pstrdup() error handling.
Style: use ngx_free() instead of free().
Core: exit on ngx_pnalloc() failure.

Signed-off-by: Piotr Sikora <piotr@cloudflare.com>
Mail: discard pipelined commands after SMTP STARTTLS.

The bug had appeared in nginx 1.5.6 (04e43d03e153).

Reported by Chris Boulton.
nginx-1.7.4-RELEASE
release-1.7.4 tag