Add a new API function SSL_CTX_use_certificate_chain() that allows to
read the PEM-encoded certificate chain from memory instead of a file.
This idea is derived from an older implementation in relayd that was
needed to use the function with a privep'ed process in a chroot.  Now
it is time to get it into LibreSSL to make the API more privsep-
friendly and to make it available for other programs and the ressl
library.

ok jsing@ miod@
Bump minor after adding SSL_CTX_use_certificate_chain().

ok jsing@ miod@