Fixes for sscanf usage:

* plugin-runner.c (main): Parse numbers correctly and portably using
                          an intermediate "intmax_t".  Cast "pid_t" to
                          "intmax_t" before passing it to "printf()".
* plugins.d/mandos-client.c (main): Parse numbers correctly and
                                    portably using an intermediate
                                    "intmax_t".  Bug fix: cast
                                    "AvahiIfIndex" to "intmax_t" and
                                    use "PRIdMAX" instead of using
                                    "PRIu16", and use "PRIu16" to
                                    format port number.
* plugins.d/splashy.c (main): Parse numbers correctly and portably
                              using an intermediate "intmax_t".
* plugins.d/usplash.c (main): - '' -