[R-Forge #5290] when called inside j, .I should be named I

[arunsrinivasan]

Submitted by: Michele Carriero; Assigned to: Arun ; R-Forge link

In the same way .N gets named as N, the same should happen for .I

dt <- data.table(a=sample(letters, 5), b=rnorm(5))
dt[, list(.N, .I)]
#    N .I
#1: 5  1
#2: 5  2
#3: 5  3
#4: 5  4
#5: 5  5