Feature Request: Extend Base.LinAlg functions

For numerical linear algebra it would be very useful to extend the implementations of `Base.LinAlg.scale!` and `Base.LinAlg.axpy!` etc. Right now, everything goes back to the implementation for AbstractArrays (which is terribly slow).

What I'm looking for is, for example:

```
using ArrayFire
using Base.Test
a = map(Float32,randn(128,128,128));
ad = AFArray(a)
t1d = Array( Base.LinAlg.axpy!(Float32(1.2),ad,ad) )
t1 = Base.LinAlg.axpy!(Float32(1.2),a ,a )
t2d = Array( Base.LinAlg.scale!(ad,Float32(2.3)))
t2 = Base.LinAlg.scale!(a, Float32,2.3))
@test_approx_eq t1 t1d
@test_approx_eq t2 t2d
```