Build OpenSSL so Ruby 2.0 installs Just Work on Mountain Lion

Ruby 2.0 won't compile the OpenSSL extension on Mountain Lion because Apple shipped a crippled OpenSSL distribution. The fix is to build your own OpenSSL and link to that instead:

```
  brew install openssl
  CONFIGURE_OPTS="--with-openssl-dir=`brew --prefix openssl`" \
    rbenv install 2.0.0-rc1
```

That's a lot of hassle for what will soon be a very common case. We can fix it by bundling a working OpenSSL.

TODO:
- [ ] The OpenSSL build needs to be limited to Mountain Lions using the crippled distribution.
- [ ] CONFIGURE_ARGS is hacked.
- [ ] And the OpenSSL configuration options need review.