added system package devscripts to r-ver/devel Dockerfile

[rnuske]

The system package devscripts contains the script checkbashisms which is now required by R CMD check --as-cran. Closes #166

[cboettig]

Thanks!

[eddelbuettel]

It is definitely good to have a check for bashisms if R(-devel) now does this. But the devscripts package has quite a footprint.

E.g. I just looked into rocker's drd image, and running apt-get install devscript would change by

Need to get 84.3 MB of archives.
After this operation, 256 MB of additional disk space will be used.

even though devscripts is only 2.5 mb it depends on a lot of other packages. Maybe we should strip out the relevant shell script only?

[eddelbuettel]

As an FYI I just had moment to look into this. For rocker/drd I took just the checkbashism file from the devscripts package and copied it in directly as it already worked in an initial test. So no additional depends required.

We may want to consider this here too. 256mb is heavy.

[eddelbuettel]

And ... of course it is checkbashisms in plural. Second commit here.

[cboettig]

Nice, yeah, I think we should be following suit in rocker-versioned as well. 256 mb is like doubling the image size here!

[eddelbuettel]

Well, that was of course relative to the smaller image I was looking at so for an already larger-one the delta may be smaller. But the general point should still hold...