Make bigger steps when calculating TTS

[Dirk Hohndel: this was sent ages ago and in all the discussions about the
               implications I apparently never applied this]

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
More tweaks to TTS calculations

Add a lager step value when walking the calculations forward.

[Dirk Hohndel: this was sent ages ago and in all the discussions about the
               implications I apparently never applied this]

Signed-off-by: Anton Lundin <glance@acc.umu.se>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Force TTS/NDL calculation off if things take too long

This is kind of a random cut off, but if plotting the dive takes more than
a second and TTS/NDL is on, we force it off. Because the algorithm for
that is fundamentally quadratic in nature it can take a VERY long time -
getting users to think something is broken.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Disclaimer included in the printed diveplan

Signed-off-by: Robert C. Helling <helling@atdotde.de>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>