The linker doesn't need the polarssl headers
Merge pull request #1915 from rubenk/dont-need-polarssl-includes-when-linking

The linker doesn't need the polarssl headers
make sure we lock the cache shards while we clean them, closing #1910. Plus add regression test that pretty reliably
detects us not locking.
Merge branch 'master' of github.com:PowerDNS/pdns
add a bunch of packet based regression tests to the packetcache
fix up our packet cache unit tests plus add bunch more tests
better key for packetcache