When pre-compiled assets are missing for the current platform, and you run gem install, the compiled native extensions are placed in the first require paths folder. This differs from rake-compiler task, where they are always placed in lib.

Setting the lib path as the first require path will ensure the compiled library is placed in the correct folder.

Allow Node tests to run with or without UV, change default version to 7, add some portability tests. Also make some more core tests work with libuv