Added make_unique() and changed cbind to use it.

[tshort]

julia> make_unique(["a", "a", "a_2", "a"])
4-element ASCIIString Array:
 "a"  
 "a_1"
 "a_2"
 "a_3"

julia> d = DataFrame({[1:4], [1:4]})
DataFrame  (4,2)
        x1 x2
[1,]     1  1
[2,]     2  2
[3,]     3  3
[4,]     4  4


julia> cbind(d,d)
DataFrame  (4,4)
        x1 x2 x1_1 x2_1
[1,]     1  1    1    1
[2,]     2  2    2    2
[3,]     3  3    3    3
[4,]     4  4    4    4

[johnmyleswhite]

Don't see any reasons not to pull this in, but I'll leave that up to @HarlanH.

[HarlanH]

Yep, looks good to me.