ITS#9326 - Renew TLS contexts on SIGUSR2

For porcess manager that want to signal cert roll-over

Note: I feel pretty audacious! This is the first time I have ever touched something like C. But hey, make builds it. But does it also do what's intended? I hope willing and knowledgeable parties would guide me a little bit so as to get this into a "works for me" patch that I could apply on custom builds, even this should be not accepted. Thanks in advance!