Fix loading certificates after tls-cert= changes (#144)

Fix loading certificates after tls-cert= changes (#144)

* Remove self-signed CA check

This check is not needed when loading the initial cert portion of a PEM file
as it will be performed later when loading the chain and was causing
self-signed CA to be rejected incorrectly.

* Fix a typo in debugs output

* Always generate static context from tls-cert= parameter

... if a cert= is provided. SSL-Bump still (for now) requires a static context as fallback when generate fails.

* Revert tlsAttemptHandshake to Squid_SSL_Accept API

* Update const correctness

* Document when initialization is skipped