Build-Depend on libssl-dev >= 0.9.8k-6.
libssl 0.9.8k-6 disabled autorenegotation, and the -dev package introduced the SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION flag. Since we now set that flag if available we want to make sure that it *is* available when building. Therefore build-depend on libssl-dev >= 0.9.8k-6. If we build against earlier versions we will not work once libssl gets upgraded to a version that disabled renegotiations.