This fixes builds after #4419. Thanks to @vbgl for the original commit;
I changed that as I'm not sure whether passing null values to buildInputs is clean.
CC maintainers: @coroa, @peti, @phreedom, @robberer, @jcumming.
There are many more packages to fix, this is just a start.
Rules:
* Don't repeat the package name (not always that easy...)
* Start with capital letter
* Don't end with full stop
* Don't start with "The ..." or "A ..."
I've also added descriptions to some packages and rewritten others.
