ZOOM now allows inspection of X509 peer certificate for verification.

ZOOM now allows inspection of X509 peer certificate for verification.
The X509 buffer is retrived by reading ZOOM option "sslPeerCert".
Removed libyazssl.la. When SSL is enabled, libyaz.la has SSL support and
all programs have too (yaz-ztest, yaz-client, zoom..). May not be
as "modular" but it simplifies things.
Added cs_get_peer_certificate to that returns peer X509 PEM.