MASTER_SITES is defined in math/R/Makefile.extension, which should be
included by all R packages. Therefore, MASTER_SITES should not normally
be defined in the Makefile for an R package.
The patch made it possible to comple R-mapdata with bmake. However, the
intent of upstream is to use gmake, which requires no patches. Therefore,
add USE_TOOLS=gmake and remove the patch.