BUG/MINOR: avoid bashism in system() call

Other shell than >=bash-4 and dash does not support '&>' I/O redirection.

Introduce in commit v0.17.5-1-g09bff77

 « While at it, I also fixed the piping of stdout and stderr to be nicer. »

src/bin/e_sys_main.c

@@ -165,7 +165,7 @@ main(int argc,
                  "-ex 'set logging file %s' "
                  "-ex 'set logging on' "
                  "-ex 'thread apply all backtrace full' "
-                 "-ex detach &> /dev/null < /dev/zero",
+                 "-ex detach > /dev/null 2>&1 < /dev/zero",
                  cmd,
 		 pid,
 		 output ?: "e-output.txt");