[PATCH] squidclient TLS support

This begins the GnuTLS library support in Squid by adding primitive TLS
support to the squidclient tool.

GnuTLS library detection is done in a compatible way such that Squid as
a whole can be built against both, either, or neither of OpenSSL and
GnuTLS. GnuTLS being FOSS and compatible license with Squid is enabled
by default when available, OpenSSL remains disabled by default due to
the licensing issues some have.

At present the library default TLS settings are used to make
connections. This tool is primarily used for debugging the HTTP messages
inside the TLS wrappings of HTTPS servers. Debugging of TLS wrappers
aroudn HTTPS is expected to come eventually, but not with this update.

Both CA verified and anonymous TLS are supported with CA verification
being the default.

The patch extends the module design by placing TLS operations and the
existing transport connection operations into a namespace/module
Transport:: .

Amos