Added PolarSSL library support to base tlsdate

The tlsdate-helper has been updated to support the entire chain of
gathering the server timestamp by using PolarSSL. Proxy support has been
disabled at this point as proxy-bio has to be rewritten or augmented to
also support a non-BIO form.
Added proxy support via a PolarSSL net-like layer
Merge pull request #71 from pjbakker/polarssl-version

Added PolarSSL library support to base tlsdate