WIP commit for pgxc_ctl.  Now tested "kill" command and fixed the program
to kill given process and its children.

	modified:   coord_cmd.c
	modified:   datanode_cmd.c
	modified:   do_command.c
	modified:   do_shell.c
	modified:   do_shell.h
	modified:   gtm_util.c
	modified:   gtm_util.h
	modified:   monitor.c
	modified:   utils.c
	modified:   utils.h