core-updates merged!

[Ludovic Courtès]

I’ve just merged core-updates in master, and Hydra has already built
most of it.  So that brings glibc 2.19, grep 2.18, libgc 7.4, guile
2.0.11, bash 6.3, the ability to use directories as package sources
(instead of tarballs), and a bunch of other updates and improvements.

It’s been more than 3 months between this merge and the previous one,
which is probably too much.

To avoid lingering branches, I think we should have a more formal,
time-based process.  For instance, we would let the branch live for N
months exactly, and freeze it at N months minus one week.

GCC and glibc are released roughly every 6 months, but typically with a
3 month offset.  So I would go for N = 2 or N = 3.  Maybe N = 2 is
better as it would allow us to make core improvements and small upgrades
more often.

Thoughts?

Thanks,
Ludo’.