dplyr:distinct is not more performant than base:unique

[ljos]

library(microbenchmark)
library(nycflights13)
library(dplyr)
tails <- select(flights, tailnum)
microbenchmark(unique(tails), distinct(tails), times=1000)

Unit: milliseconds
            expr       min       lq     mean   median       uq      max neval
   unique(tails)  8.728119 10.25836 12.32073 11.92595 13.18344 73.76151  1000
 distinct(tails) 49.051397 51.84157 53.33416 52.98128 54.06816 67.46064  1000

R version:
x86_64, darwin15.0.0
R version 3.2.2 (2015-08-14)
Fire Safety
(Built with openblas)

dplyr version:
0.4.3.9000
(Installed with devtools::install_github() on 2015.11.08)

[romainfrancois]

related to #977