Fix warning related to registration of native routines

[jefferis]

Latest r-devel (as of 20 Feb 2017) has a problem.

Result: NOTE 
    File ‘nabor/libs/nabor.so’:
     Found no calls to: ‘R_registerRoutines’, ‘R_useDynamicSymbols’
    
    It is good practice to register native routines and to disable symbol
    search.

See:

https://cran.r-project.org/web/checks/check_results_jefferis_at_gmail.com.html#nabor

RcppCore/Rcpp#636

[jefferis]

See RcppCore/Rcpp#636

[jefferis]

See https://www.mail-archive.com/rcpp-devel@lists.r-forge.r-project.org/msg09132.html for discussion and a possible solution for modules. Just running

> tools::package_native_routine_registration_skeleton('.')
#include <R.h>
#include <Rinternals.h>
#include <stdlib.h> // for NULL
#include <R_ext/Rdynload.h>

/* FIXME: 
   Check these declarations against the C/Fortran source code.
*/

/* .Call calls */
extern SEXP nabor_knn_generic(SEXP, SEXP, SEXP, SEXP, SEXP);

static const R_CallMethodDef CallEntries[] = {
    {"nabor_knn_generic", (DL_FUNC) &nabor_knn_generic, 5},
    {NULL, NULL, 0}
};

void R_init_nabor(DllInfo *dll)
{
    R_registerRoutines(dll, NULL, CallEntries, NULL, NULL);
    R_useDynamicSymbols(dll, FALSE);
}

produced an init.c that gave a module loading error exactly as described in the mailing list message linked above.

[jefferis]

This is the stripped down version

#include <R.h>
#include <Rinternals.h>
#include <stdlib.h> // for NULL
#include <R_ext/Rdynload.h>

void R_init_nabor(DllInfo *dll)
{
    R_registerRoutines(dll, NULL, NULL, NULL, NULL);
    R_useDynamicSymbols(dll, TRUE);
}

[jefferis]

Note that I did not do useDynLib(nabor, .registration=TRUE) in the NAMESPACE.