Re: Support for NSS as a libpq TLS backend

Attached is a rebase to keep bitrot at bay.  On top rebasing and smaller fixes
in comments etc, this version fixes/adds a number things:

* Performs DN resolution to support the DN mapping
* Locks the SECMOD parts and PR_Init call in the frontend as per Jacobs
  findings upthread
* Properly set the tokenname of the database to avoid ambigious lookups in case
  multiple databases are loaded (a better name to ensure uniqueness is a TODO)
* Adds a test for certificate lookup without sslcert set



--
Daniel Gustafsson        https://vmware.com/