Bug #179: Use of the data type "sig_atomic_t" for a few variables

Now the data type "sig_atomic_t" is used for the safe exchange of integral data
with signal handlers.
http://www.gnu.org/software/libc/manual/html_node/Atomic-Types.html

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Merge pull request #182 from elfring/fix_signal_handler

Use of the data type "sig_atomic_t" for a few variables.

Fixes #179.