radix 4 now about as fast as original version
radix 4 now about as fast as original version

'make test' output:
### testing SNR for  1024 point FFTs
#### DOUBLE
snr_t2f = 296.78
snr_f2t = 317.11
#### FLOAT
snr_t2f = 145.28
snr_f2t = 143.51
#### SHORT
snr_t2f = 52.409
snr_f2t = 22.174

#### timing 10000 x 1024 point FFTs
#### DOUBLE
Elapsed:0:03.43 user:2.68 sys:0.25
#### FLOAT
Elapsed:0:01.39 user:1.08 sys:0.11
#### SHORT
Elapsed:0:02.01 user:1.39 sys:0.09

CBL-ORION/kiss-fft,CBL-ORION/kiss-fft,CBL-ORION/kiss-fft,CBL-ORION/kiss-fft