[LinuxCNC/linuxcnc PR#65] Seb/2.6/task cleanups

These are all minor changes that I plan to merge into 2.6, but they touch sensitive areas for such an old stable branch so I’d appreciate more eyeballs on it as a sanity check.

These commits all came out of debugging for #49 and the statbuf-g5x-abort bug that Zultron reported. This branch does not fix those problems, but these commits are generally useful on their own.