TerraGear Merge Request #24: Using abs() for double argument caused segfault in genapts (merged)

Running genapts caused a segmentation fault, which was tracked down to zero values for nrm (line 76 in jama_qr.h) being stored in Rdiag, leading qr.solve to decide the matrix was rank deficient and therefore returning an empty solution. The zero values arose because, when abs() was called on a small double in the hypot() function, it returned 0, and if all values were sufficiently small, nrm remains at zero.

This fix simply replaces abs() with fabs().