Work around missing function support

[dominicletz]

This fixes two issues:

1. crypto.hash_equals can be present but unsupported (in which case it throws)

2. When compiling beam files on a newer otp revision than deploying , the compile time detection reports false positives. Instead we're using runtime detection now always.

[josevalim]

When compiling beam files on a newer otp revision than deploying , the compile time detection reports false positives. Instead we're using runtime detection now always.

We can expand on this a bit? I don't believe Elixir nor the Erlang VM actually supports compiling on a newer OTP version. You should always compile on the lowest version that you plan to support.