names_c: Extract function table from names.c from R subversion repository.

Description

Since this is an expensive operation, it is done once and cached within a session.

names_c()

A data frame with columns

name: the function name in R
c-entry: The name of the corresponding C function, actually declared in ../include/Internal.h. All start with "do_", return SEXP, and have argument list (SEXP call, SEXP op, SEXP args, SEXP env)
offset: the 'op' (offset pointer) above; used for C functions which deal with more than one R function
eval: XYZ (three digits)

X=0 says that we should force R_Visible on
X=1 says that we should force R_Visible off
X=2 says that we should switch R_Visible on but let the C code update it.

Y=1 says that this is an internal function which must be accessed with a .Internal(.) call, any other value is accessible directly and printed in R as ".Primitive(..)".

Z=0 says don't evaluate (SPECIALSXP).
Z=1 says evaluate arguments before calling (BUILTINSXP)
arity: How many arguments are required/allowed; "-1" meaning ``any''
pp-kind: Deparsing Info (-> PPkind in ../include/Defn.h )
precedence: Operator precedence (-> PPprec in ../include/Defn.h )
rightassoc: Right or left associative operator