WIP: generic number type2

work in progress, not ready for merging

continuing from here: https://github.com/ApproxFun/ApproxFun.jl/pull/71


I have made a mistake in writing `chebyshevtransform` in terms of fft and was hoping for help. As far as I can tell, the `fft_gen` and `ifft_gen` functions are working properly. I wrote `chebyshevtransform` to match https://github.com/chebfun/chebfun/blob/master/@chebtech2/vals2coeffs.m , but I didn't really understand what I was doing.

```julia
julia> n = 8; r = BigFloat[BigFloat(r) for r in rand(n,)];

julia> maximum( abs(chebyshevtransform(r) - chebyshevtransform(float64(r))) )
9.025352232940452587915806506104435996422000032418633430176793848182664747881608e-02 with 256 bits of precision
```
Thanks for spotting that! That was indeed the problem.

You should be able to pull this branch, but just be careful not to clobber any of your own files.

go into `~/.julia/v0.3/ApproxFun` 
and run 
`git remote add goretkinbranch_oranynameyoulike https://github.com/goretkin/ApproxFun.jl`
and check that `git remote -v` shows the appropriate remote repositories

then `git fetch goretkinbranch_oranynameyoulike`

so far, none of your files risk getting clobbered.

finally,  `git checkout goretkinbranch_oranynameyoulike/general_number`. Git should warn you if you have any modified files `error: Your local changes to the following files would be overwritten by checkout`