support for newer SSL certificate types

more and more CAs are using certificates signed using SHA256 or SHA512,
whereas go's X.509 support by default only supports certificates signed
with a SHA1 hash.

Importing the two hashes causes them to be registered and available to
use for x509 which in turn allows connecting to servers using one of
these newer certificates
Merge pull request #188 from pilif/support-more-ssl-cert-hashes

support for newer SSL certificate types
Enable build on freebsd (#132 / #112)
Enable build on openbsd to fix #194
Fix state file persistence
Merge pull request #198 from driskell/bugs/statefile_persistence

Fix state file persistence
Only clean out prospector info of files we've stopped harvesting
Remove obsolete statement
Remove offset channel from harvester directly to registrar
Tidy and improve variable naming
Remove redundant comment
Merge branch 'tzahari/master' into driskell
Tidy registrar
Tweak startup events and always write registry
Merge branch 'master' of https://github.com/elasticsearch/logstash-forwarder into driskell
Merge branch 'driskell' into driskell_merge_pr164
(This is the new 'driskell' branch which was rebuilt for PR - thus conflicts had to be resolved and there may be duplicate commits in the history)