DOCUMENT: TMPDIR to control tempdir() may be set in .Renviron

[HenrikBengtsson]

The following should be added to a Section "Known limitations" in README:

• [x] TMPDIR to control tempdir() may be set in .Renviron but not "later" must be set prior to launching R. For instance, using Sys.setenv(TMPDIR="/path/to") in .Rprofile won't work. This also means that it does not work to set in ~/.Renviron.d/tempdir that startup::startup() processes.

[HenrikBengtsson]

• [x] R_DEFAULT_PACKAGES
• [x] R_LIBS_USER

can be set in .Rprofile but not later.

[HenrikBengtsson]

Another example is

• [x] OMP_NUM_THREADS, cf. http://heather.cs.ucdavis.edu/~matloff/rth.html

[HenrikBengtsson]

Another environment variable that is utilized only early on in the R startup processes and that can not be updated later is

• [x] R_MAX_NUM_DLLS.