(ITS#6969) Need option to show which TLS library is in use

[hyc@OpenLDAP.org]

Full_Name: Howard Chu
Version: 2.4/HEAD
OS: 
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (76.94.188.8)
Submitted by: hyc


Now that OpenSSL is not the only TLS library that we support, app developers
need a way to check which library is in use. libldap has the info, but due to an
oversight it was not exposed.

The LDAP_OPT_X_TLS_PACKAGE option has been added to retrieve the TLS
implementation name. Currently it may be "OpenSSL", "GnuTLS", or "MozNSS".