Replaced hard coded SSL_VERSIONS for introspecting into OpenSSL SSL_VERSIONS.

- Doing it this way makes HTTPI compatible with Ruby 1.9.x-2.1.x
- It will automatically pick up newer TLS versions.
Added Ruby 2.x SSL versions to the curb adapter.

- Based on my understanding, curl will use the best available version of
  TlS. I assume that curb does the same.
- In Ruby 2.x there are SSLv3 and SSLv23. I assume that SSLv23 would be
  the only option for SSLv2.
Fixed specs to account for dynamic introspection of SSL_VERSIONS.

- Since we're no longer hard coding values, our tests need to account
  for that.
- A few tests were removed for a single generic test as we really only
  need to test a getter and setter once, rather than testing for every
  possible value.
Merge pull request #136 from saghaulor/refactor_ssl_to_dynamically_introspect_ssl_version_from_openssl

Refactor ssl to dynamically introspect ssl version from openssl