Unnamed matrices resulting misleadingly-labelled outputs

[MichaelChirico]

Noticed while working on #174

writeLines(repr(matrix(ncol = 100L)))
#      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14] [,15] [,16] [,17] [,18] [,19] [,20] [,21]
# [1,] NA   NA   NA   NA   NA   NA   NA   NA   NA   NA    ⋯     NA    NA    NA    NA    NA    NA    NA    NA    NA    NA   

• Ideally those numbers would refer to the actual column numbers, not the elided ones
• Even allowing that we can refer to the elided column numbers, ... is counted as getting its own column, so the numbers are still off-by-one.