README: Update section on plugins with info on hooks and I/O plugins.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
run_interactive(): Fix file descriptor leak when debug is enabled.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
touch(): Check return value of mknod(), report error if errno != EEXIST.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
pidfile_read(): Fix potential integer overflow when reading PID

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>