Find shadowed packages

[Enchufa2]

Here's my version, closes #58. I opted for one package per line, and the idea is that Package in LibPath is shadowed by the one in Shadow.LibPath, which has higher priority (the one that casts its shadow). Shadow.Newer is TRUE when the Shadow.Version is newer (and therefore shadowing would be acceptable). @eddelbuettel @MatthieuStigler Comments welcome.

Sample output:

bspm::shadowed_packages()
#>               Package              LibPath  Version           Shadow.LibPath Shadow.Version Shadow.Newer
#> base64enc   base64enc /usr/lib64/R/library    0.1.3 /usr/local/lib/R/library          0.1.3        FALSE
#> boot             boot /usr/lib64/R/library   1.3.28 /usr/local/lib/R/library       1.3.28.1         TRUE
#> cachem         cachem /usr/lib64/R/library    1.0.6 /usr/local/lib/R/library          1.0.6        FALSE
#> class           class /usr/lib64/R/library   7.3.20 /usr/local/lib/R/library         7.3.21         TRUE
#> cluster       cluster /usr/lib64/R/library    2.1.4 /usr/local/lib/R/library          2.1.4        FALSE
#> codetools   codetools /usr/lib64/R/library   0.2.18 /usr/local/lib/R/library         0.2.18        FALSE
#> digest         digest /usr/lib64/R/library   0.6.29 /usr/local/lib/R/library         0.6.31         TRUE
#> fastmap       fastmap /usr/lib64/R/library    1.1.0 /usr/local/lib/R/library          1.1.0        FALSE
#> foreign       foreign /usr/lib64/R/library   0.8.83 /usr/local/lib/R/library         0.8.84         TRUE

[eddelbuettel]

I'll try to take a look later. I agree that one these could and should be in bspm and I also thought about the 'long-to-wide' transformation you did here.

[Enchufa2]

Merging here. We can revisit later if we find any sharp edge.