[cctbxbb] Not wishing to raise this again but...

[Marcin Wojdyr]

While I don't contribute anything substantial to cctbx, a few months
ago I ran cctbx tests after building Dials and wanted to make a couple
of trivial fixes.
I made a change and tried to commit it, but it didn't work - because I
did checkout anonymously. So I spent a few minutes googling how to do
authenticated commit from anonymously checked out sources, found
nothing (I'm sure there is a way, but I didn't want to waste more time
on it) and finally I copied the modified files to a laptop that I
previously used to commit to cctbx and committed it from there.
It's easier to contribute a change to a random project on Github. Not
because the process in itself is simpler (fork, new branch, commit,
push, pull request), but because it's the same process as for majority
of other projects nowadays. Moving to Github lowers the entry barrier
- for good and bad.

Regarding boost, ccp4io_adaptbx, etc: I generally agree with Luc, but
adding subtrees and submodules will make working with the repository
more complex. No idea how it's mapped to svn for those who'd prefer to
keep using svn. It'd be simpler to avoid subtrees and have
ccp4io_adaptbx and other non-external modules in the main cctbx repo
(it should be technically doable during the migration).

Marcin