More loops

[tedbauer]

Some of the MachSuite apps require loops that aren't supported in Fuse. AFAIK we only allow looping over ranges. Here are some loops that I think we can't write yet:

• while(a_idx>0 || b_idx>0) { ... } (From nw/nw, a "dynamic programming algorithm for optimal sequence alignment.") (Do we have boolean operators like "and" and "or"?)
• for(span=FFT_SIZE>>1; span; span>>=1, log++){ ... } (From fft/strided, a "recursive formulation of the Fast Fourier Transform.")

[rachitnigam]

Split into #63 and #72.