Each R package should include ../../math/R/Makefile.extension, which also
defines MASTER_SITES. Consequently, it is redundant for the individual
packages to do the same. Package-specific definitions also prevent
redefining MASTER_SITES in a single common place.
An alternative approach to non-standard evaluation using
formulas. Provides a full implementation of LISP style
'quasiquotation', making it easier to generate code with other code.