tweak error handling when reading the pid file

previously strtol() would look at unitialized
storage, but now the string is terminated where
the data read ends

give user a hint about removing the file if we can't
read/parse it properly

(somehow I ended up with a truncated httpd.pid on my
own system, leading to these tweaks)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@104651 13f79535-47bb-0310-9956-ffa450edef68