used += on complex components
used += on complex components


dramatic speedup -- 'make test' output:
### testing SNR for  1024 point FFTs
#### DOUBLE
snr_t2f = 295.63
snr_f2t = 307.82
#### FLOAT
snr_t2f = 146.25
snr_f2t = 143.37
#### SHORT
snr_t2f = 54.694
snr_f2t = 24.470

#### timing 10000 x 1024 point FFTs
#### DOUBLE
Elapsed:0:16.06 user:12.72 sys:0.25
#### FLOAT
Elapsed:0:04.63 user:3.79 sys:0.13
#### SHORT
Elapsed:0:05.77 user:4.56 sys:0.07

sf-is-evil/kissfft,sf-is-evil/kissfft,pemryan/kissFFT,pemryan/kissFFT,pemryan/kissFFT,pemryan/kissFFT,sf-is-evil/kissfft,sf-is-evil/kissfft