Reusing Bitcoin Core's Gitian dependency cache about namecoin-core

[josephbisch]

Looks like it is just the name: https://github.com/devrandom/gitian-builder/blob/923016ec8d1abb127c92a127a527f71c67d78acf/bin/gbuild#L83.

[JeremyRand]

I changed the name to use "bitcoin" instead of "namecoin". This did make Gitian reuse the dependency cache, but the build failed (seemed to have trouble finding a Qt header). I'll come back to this later, but for now I think we'll avoid making this change.

[domob1812]

@JeremyRand, is this still relevant (and if so, do you plan to work on this)?

[JeremyRand]

It's probably still relevant, and it would be great if someone wants to experiment with this, but I'm not likely to have time to touch this in the next couple months.