Build & reload via CTRL + SHFT + B comes back with an error due to supposed library mismatch

Hi Kevin,

I just noticed that when enabling packrat (and thus internally switching to the packrat package libraries), a build & reload via CTRL + SHFT + B (and using roxygen2) comes back with an error as the package is built to either the user or system library, but not to the packrat library, which, in turn is being used/queried again when R calls library(pkgname) at the end of the build & reload cycle (which of course fails.

> sessionInfo()
R version 3.3.2 (2016-10-31)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)

locale:
[1] LC_COLLATE=German_Germany.1252  LC_CTYPE=German_Germany.1252    LC_MONETARY=German_Germany.1252
[4] LC_NUMERIC=C                    LC_TIME=German_Germany.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] testthat_1.0.2  roxygen2_5.0.1  devtools_1.12.0

loaded via a namespace (and not attached):
 [1] R6_2.2.0        magrittr_1.5    tools_3.3.2     withr_1.0.2     crayon_1.3.2    Rcpp_0.12.8    
 [7] memoise_1.0.0   stringi_1.1.2   stringr_1.1.0   digest_0.6.10   packrat_0.4.8-1

Reproduce the CTRL + SHFT + B build-and-reload flow with packrat and roxygen2 on the reported Windows/R setup. Trace where the package is built versus where the final library(pkgname) lookup searches. Done means the reload completes without a library mismatch error and loads the package from the expected library.