both FFTW and Base export "FFTW"

Been trying to get some code running on v0.7 and running into difficulties with getting FFTW to work in my modules. Here is a simplified module that gives me errors.

```
module Fields

export r𝔽, Flat

using FFTW
import Base: *, \

abstract type Flat{Θpix,nside} end

struct r𝔽{P<:Flat,T<:Real,F}
Δx::T
Δk::T
Ωk::T
Ωx::T
period::T
nyq::T
k::Vector{Matrix{T}}
x::Vector{Matrix{T}}
FFT::F
end

# real FFT generated function constructor
@generated function r𝔽(::Type{P},::Type{T}) where T<:Real where P<:Flat{Θpix, nside} where {Θpix, nside}
Δx = deg2rad(Θpix/60)
period = Δx*nside
Δk = 2π/period
Ωk = Δk^2
Ωx = Δx^2
nyq = 2π / (2Δx)
k_side = ifftshift(-nside÷2:(nside-1)÷2) * Δk
x_side = ifftshift(-nside÷2:(nside-1)÷2) * Δx
k = [reshape(k_side, 1, nside), reshape(k_side[1:nside÷2+1], nside÷2+1, 1)]
x = [reshape(x_side, 1, nside), reshape(x_side, nside, 1)]
FFT = Ωx / (2π) * plan_rfft(rand(T,nside,nside); flags=FFTW.PATIENT, timelimit=4)
r𝔽{P,T,typeof(FFT)}(Δx, Δk, Ωk, Ωx, period, nyq, k, x, FFT)
end

(*)(g::r𝔽{P,T}, x) where P<:Flat where T = g.FFT * x
(\)(g::r𝔽{P,T}, x) where P<:Flat where T = g.FFT \ x

end
```

I want the following code block to run ...

```
using Main.Fields

nside = 1024
Θpix = 2.0
Px = Flat{Θpix,nside}
Tx = Float32
g = r𝔽(Px,Tx)

fx = rand(nside, nside)
fk = g * fx
y = g \ fk
```

.... but I get the following error in the line:

```
julia> g = r𝔽(Px,Tx)
WARNING: both FFTW and Base export "FFTW"; uses of it in module Fields must be qualified
ERROR: UndefVarError: FFTW not defined
Stacktrace:
[1] #s1#1(::Any, ::Any, ::Any, ::Any, ::Any, ::Type, ::Any) at ./REPL[1]:34
[2] (::Core.GeneratedFunctionStub)(::Any, ::Vararg{Any,N} where N) at ./boot.jl:443
[3] In toplevel scope

```

Any ideas what is going on?

Here is my version info:
```
julia> versioninfo()
Julia Version 0.7.0-DEV.2454
Commit 00dafe28c0* (2017-11-07 15:53 UTC)
Platform Info:
OS: macOS (x86_64-apple-darwin17.2.0)
CPU: Intel(R) Core(TM) i7-5557U CPU @ 3.10GHz
WORD_SIZE: 64
BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Haswell)
LAPACK: libopenblas64_
LIBM: libopenlibm
LLVM: libLLVM-3.9.1 (ORCJIT, broadwell)
```