added complexconjugate as method
FFTConvolution now works correctly. Thanks a lot for pointing out this long-standing bug
Christian Dietz!

Now the complexconjugate is computed before multiplying in fourier space, this corresponds
to mirroring the kernel in real space. It can be turned off for performance reasons if
(a) the kernel is symetric anyways (b) the kernel is already mirrored
Merge branch 'master' of github.com:imagej/imglib