In 2.0, the distance between the points in the TTF request specified
cap height. In 2.1, that was accidentally changed to some arbitrary
value near cap height instead, due to a 72pt factor mess-up.
This commit restores the old behavior.
If SolveSpace crashes after the open, or hangs and is forcibly
killed, data would be lost. (I lost my data.) Instead, remove
autosave only in two cases: right after a successful save, or right
after a save is declined. This should be completely safe.