Linting guix packages

Guix is getting more mature every day (It's probably going to beta soonish).  One of the commands it got 'recently' is guix lint.

Once you write a package definition you want to know if it complies with guix standards. Let's try guix lint.

1. Write package definition.
2. Put the definition into a guix checkout (not your running guix).
3. run 'guix environment guix'.
4. cd to the checkout directory.
5. ./bootstrap && ./configure --localstatedir=/var --prefix= && make
6. ./pre-inst-env guix lint my-package
7.  If you get an 'ERROR: missing interface for module (gnutls)', means that you need to install gnutls. 'guix package -i gnutls'
8. After that, you can finally run 'guix lint my-package', and it'll tell you if you have any obvious failures or warnings in your definition.