ruby: fixes rubygems user installs

* Manage patches in git
* Fixes the hook invocation to be more safe. Thanks @Mic92
* Install gems as user by default
* Install gem binaries with the /usr/bin/env shebang
* Fixes a bug where the passthru.libPath and passthru.gemPath would
  point to the wrong directory
* Overhaul ruby version heuristics