tweak error handling when reading the pid file

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