making string_proxy::operator==( string_proxy ) const to disambiguate

[romainfrancois]

Fixes #854

#include <algorithm>
#include <Rcpp.h>
using namespace Rcpp ;

// [[Rcpp::export]]
bool test(CharacterVector x, CharacterVector y) {
    if (x.length() != y.length()) {
        return false;
    }

    return std::equal(x.begin(), x.end(), y.begin());
}


/*** R
test("foo", "bar")
*/

gives :

romain@purrplex ~/git/RcppCore $ Rscript -e 'Rcpp::sourceCpp("~/Desktop/test.cpp")'

> test("foo", "bar")
[1] FALSE

[eddelbuettel]

Thumbs up, all good.