exceptions in kde

[alang9]

Maybe these should be two separate issues, but here goes:

> let f x y = kde x $ Data.Vector.Unboxed.replicate y 0.0
> f 2 1
(fromList [-0.1,0.1],fromList [6.255700138464551,3.744299861535448])
> f 1 1
*** Exception: Statistics.Math.log2: invalid input
> f 1 2
*** Exception: ./Data/Vector/Generic/Mutable.hs:576 (read): index out of bounds (-9223372036854775808,1)

[Shimuuar]

dct is at fault.

>>> dct $ U.replicate 1 0
*** Exception: Statistics.Math.log2: invalid input

Even worse:
>>> dct $ U.replicate 3 0
[0.0,0.0]

Reordering of vector's elements in the dctWorker works improperly for samples with odd sizes