Unified string handling.

Unified string handling.

sstrncpy() and the newly added function ssnprintf() are now used all over
the place to make sure strings are null terminated. This removes quite
some duplicate code that was found all over the place and thus fairly
increases overall readability of the code. Also sizeof() is used instead
of hard-coded constants where appropriate to determine the available
space.

Signed-off-by: Sebastian Harl <sh@tokkee.org>
Signed-off-by: Florian Forster <octo@huhu.verplant.org>