Just because a package has a preinstall doesn't mean it doesn't have a gypfile

[gabrielschulhof]

Related issues:

npm/npm#12133
npm/normalize-package-data#75

This package also makes the assumption that the presence of a preinstall script means that the package does not use a gyp file and that the default install script for such a package (node-gyp rebuild) does not need to be run.

This is an unnecessary assumption and one that breaks my package.

In my tests, when I remove this assumption, my package builds fine. Would it be possible to remove this assumption?