add a tlmgr_repo function to query or set CTAN repository

the bug in `tlmgr info --list --data relocatable` has been fixed, so remove this patch, and add a test so that we will be able to discover this problem if it occurs again

remove the patch introduced in d9ed3c4; the problem seesm to have been fixed upstream

one more package: https://travis-ci.com/github/yihui/tinytex/jobs/396082629

add/remove R's texmf tree quietly

patch tlmgr.pl on Windows to avoid the false alarm: http://www.tug.org/svn/texlive/trunk/Master/texmf-dist/scripts/texlive/tlmgr.pl?r1=56562&r2=56561&pathrev=56562