Merge new pre_install_check.js [replaces pre_install_check.sh]

[johannish]

Because the pre_install_check.sh must be sourced, it receives all environment variables as set for the current shell. However, node-gyp itself will run in a sub-shell and may not see the same variables.

This caused an issue for me just now where I had set OCI_LIB_DIR=... in my .bashrc without the export command. Thus, pre_install_check.sh reported that everything was okay, even though node-gyp could not see those same environment variables.

[johannish]

Ha! So I just realized that this was fixed by the further work you did back in February, @vrvolle. I'll work on merging those changes in and testing the full workflow.