Bug #27: Reuse of the data type "sig_atomic_t"

Two variables are used in signal handler implementations. Their data type
was set to sig_atomic_t to improve software portability.
http://en.cppreference.com/w/c/program/sig_atomic_t

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Merge pull request #39 from elfring/Reuse_of_sig_atomic_t

Reuse of the data type "sig_atomic_t"