Ticket #1521: ctrl-z (aka suspend) does not work

Fix issue:
execute.c is missing #include <signal.h> and therefore #ifdef SIGTSTP fails miserably.

Signed-off-by: Slava Zanko <slavazanko@gmail.com>

src/execute.c

@@ -21,6 +21,7 @@
 
 #include <config.h>
 
+#include <signal.h>
 #include <sys/stat.h>
 #include <sys/time.h>