I noticed that `maximum!(v, A)`

is slower than my following implementation, I couldn’t find its implementation in Base to check my self.

```
function maximum2!(out,A)
@inbounds for i = 1:length(out)
out[i] = A[i]
end
@inbounds for j = 2:size(A,2)
for i = 1:size(A,1)
out[i] = ifelse(A[i,j] > out[i], A[i,j], out[i])
end
end
out
end
```

I measured the performance of both functions as follows, finding my function to be 4.2X faster:

```
using BenchmarkTools
srand(1234)
const A = randn(1000,1000)
const v = Array{Float64}(uninitialized, 1000)
@btime maximum!(v, A)
@btime maximum2!(v, A)
1.025 ms (7 allocations: 288 bytes)
244.020 μs (0 allocations: 0 bytes)
```

Do I miss something?