OpenSSL depenency management.

[ben-crowhurst]

Currently we don't pull down OpenSSL when cloning the repository. And we don't force the dependency to build if we fail to locate a preinstalled installation.

How should we manage this dependency?

1. User instructions?
2. CMake ExternalProject_Add?
3. Other?

[ben-crowhurst]

Latest version of OpenSSL causes issues with ASIO; See here for details.

*) config has been changed so that by default OPENSSL_NO_DEPRECATED is used.
     Access to deprecated functions can be re-enabled by running config with
     "enable-deprecated". In addition applications wishing to use deprecated
     functions must define OPENSSL_USE_DEPRECATED. Note that this new behaviour
     will, by default, disable some transitive includes that previously existed
     in the header files (e.g. ec.h will no longer, by default, include bn.h)
     [Matt Caswell]

To build OpenSSL on Mac OS X you'll require the following configure command:

./Configure darwin64-x86_64-cc enable-ec_nistp_64_gcc_128

Elsewhere its:

./config

See here for build options.

[ben-crowhurst]

We've decided not to automate the construction of OpenSSL. There are far too many options to best guess a reasonable subset for most business cases.

A git submodule representing the supported version of OpenSSL has been include within the project.