[GRASS-stats] rgrass7: simplify initGRASS for Windows OSGeo4W users

[Roger Bivand]

Windows OSGeo4W users often are confused when trying to use
rgrass7::initGRASS() in Rgui, RStudio, or console R, because R was not
started in the OSGeo4W console. We see this for example in threads
leading up to:

https://lists.osgeo.org/pipermail/grass-stats/2018-November/001800.html

also with pop-up errors. Recently, this re-appeared in:

https://github.com/rsbivand/rgrass7/issues/16

After testing with 32-bit and 64-bit OSGeo4W, it seems that the draft
rgrass7 version that can be downloaded from

https://win-builder.r-project.org/cMvPja6B7kpy/

should provide more guidance, first stopping initGRASS() as early as
possible when OGGEO4W_ROOT is not set (the OSGeo4W shell sets it
correctly), and providing an explanation in the initGRASS help page.

If you use OSGeo4W and rgrass7, please test this draft version, and
report, especially if the changes impact your workflow in a negative way.
If there are no problems, this version will be submitted to CRAN soon.

Best wishes,

Roger

-- 
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; e-mail: Roger.Bivand at nhh.no
https://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en