[sane-devel] Fix signal handler

[Markus Elfring]

Hello!

The functions "exit()" and "free()" do not belong to the list of 
async-signal-safe functions. (They are called by "xsane_quit()". )
See section "2.4.3 Signal Actions" from the document "2.4 Signal Concepts".
http://opengroup.org/onlinepubs/009695399/functions/xsh_chap02_04.html#tag_02_04_03
http://opengroup.org/onlinepubs/009695399/functions/_Exit.html

I guess that a different program design will be needed for your 
functions "xsane_sigchld_handler" and "xsane_quit_handler".
http://xsane.org/download/xsane-0.994.tar.gz

Regards,
Markus