Divelogs.de: prevent undefined behaviour

prepare_dives_for_divelogs() did a silly thing, which I was
responsible for. When populating 'tempfile' we benefit
from QString, but then return a pointer to a local variable
(char *) without alocating it on the heap. This resulted
in undefined behavior, as we don't know the lifespan of that
local memory on the stack.

Patch fixes that by using strdup() and freeing the memory
when/if needed.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
User manual: remove imperative not to save

It's ok to save as you go, just not required.

Signed-off-by: Tim Wootton <tim@tee-jay.demon.co.uk>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
User manual: use charge rather than load when referring to battery

Signed-off-by: Tim Wootton <tim@tee-jay.demon.co.uk>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>