Drop direct use of NAMED

Since data.table now depends on R >= 3.3, the backports are no longer
needed. Moreover, MAYBE_SHARED is currently a function, while
MAYBE_REFERENCED expands to !NO_REFERENCES (which is a function).

In debugging output, show MAYBE_REFERENCED (NAMED > 0) instead of NAMED.

Author: aitap

src/assign.c

@@ -549,12 +549,12 @@ SEXP assign(SEXP dt, SEXP rows, SEXP cols, SEXP newcolnames, SEXP values)
          (TYPEOF(values)!=VECSXP && i>0) // assigning the same values to a second column. Have to ensure a copy #2540
          ) {
         if (verbose) {
-          Rprintf(_("RHS for item %d has been duplicated because NAMED==%d MAYBE_SHARED==%d, but then is being plonked. length(values)==%d; length(cols)==%d)\n"),
-                  i+1, NAMED(thisvalue), MAYBE_SHARED(thisvalue), length(values), length(cols));
+          Rprintf(_("RHS for item %d has been duplicated because MAYBE_REFERENCED==%d MAYBE_SHARED==%d, but then is being plonked. length(values)==%d; length(cols)==%d)\n"),
+                  i+1, MAYBE_REFERENCED(thisvalue), MAYBE_SHARED(thisvalue), length(values), length(cols));
         }
         thisvalue = copyAsPlain(thisvalue);   // PROTECT not needed as assigned as element to protected list below.
       } else {
-        if (verbose) Rprintf(_("Direct plonk of unnamed RHS, no copy. NAMED==%d, MAYBE_SHARED==%d\n"), NAMED(thisvalue), MAYBE_SHARED(thisvalue));  // e.g. DT[,a:=as.character(a)] as tested by 754.5
+        if (verbose) Rprintf(_("Direct plonk of unnamed RHS, no copy. MAYBE_REFERENCED==%d, MAYBE_SHARED==%d\n"), MAYBE_REFERENCED(thisvalue), MAYBE_SHARED(thisvalue));  // e.g. DT[,a:=as.character(a)] as tested by 754.5
       }
       SET_VECTOR_ELT(dt, coln, thisvalue);                 // plonk new column in as it's already the correct length
       setAttrib(thisvalue, R_NamesSymbol, R_NilValue);     // clear names such as  DT[,a:=mapvector[a]]

src/data.table.h

@@ -60,14 +60,6 @@
 // for use with CPLXSXP, no macro provided by R internals
 #define ISNAN_COMPLEX(x) (ISNAN((x).r) || ISNAN((x).i)) // TRUE if either real or imaginary component is NA or NaN
 
-// Backport macros added to R in 2017 so we don't need to update dependency from R 3.0.0
-#ifndef MAYBE_SHARED
-#  define MAYBE_SHARED(x) (NAMED(x) > 1)
-#endif
-#ifndef MAYBE_REFERENCED
-#  define MAYBE_REFERENCED(x) ( NAMED(x) > 0 )
-#endif
-
 // If we find a non-ASCII, non-NA, non-UTF8 encoding, we try to convert it to UTF8. That is, marked non-ascii/non-UTF8 encodings will
 // always be checked in UTF8 locale. This seems to be the best fix Arun could think of to put the encoding issues to rest.
 // Since the if-statement will fail with the first condition check in "normal" ASCII cases, there shouldn't be huge penalty issues in