revised version of wavelet transform

[Brian Gough]

I've had a look at this now.  It is a good improvement.

A couple of points I noticed,

- in the initialisation of h1, h2, g1, g2 in daubechies and bspline
there are non-constant static arrays, which are not thread-safe.  To
avoid this, I'd recommend supplying all the coefficients as
precomputed tables (even though they only differ in sign).

- there could be some value in putting the allowed wavelet lengths in
an array in the wavelet_type struct, to allow a calling routine to
inspect them. The array could be terminated with 0.

-- 
Brian