Actual implementation is in OpenSSL subclass. This allows a permanent vector of shared certificates to be used when creating multiple OpenSSL contexts. This replaces the existing use of a vector of unique pointers to certificates which handed over responsibility for the underlying OpenSSL certs to the OpenSSL context. To enable this to work, a new method is added to the OpenSSLCertificate class which enables the reference count on the the contained OpenSSL certificate to be incremented - this stops the OpenSSL certificate being deleted when the OpenSSL context is freed. Use of conditional compilation was necessary to get the reference counting to build with the different versions of OpenSSL in use. Modify the method in OpenSSLCertificateFactory (and stub in CertificateFactory) which generates a vector of certificates, so that it generates a vector of shared_ptrs rather than unique_ptrs. Add test of CreateCertificateChain to Swiften CertificateTest class, together with sample certificate file in PEM form. JIRA: LINK-1763 Bug: Release-notes: Manual: Test-information: Tested via development version of Mystique - created multiple TLS sessions using single certificate chain. Swift unit tests now build and run again. New Swiften TLS unit test builds and runs. Change-Id: I7fa4888b640c94b68712a6bff1f7aa334a358df2