The "--serverip" and "--requestedip" options now accept host names, too.

The "--serverip" and "--requestedip" options now accept host names, too.
This doesn't quite fit the option names and so far I haven't changed the
"--help" output which currently only talks about IP addresses.  However,
I don't see why resolving host names should not be supported.

Also note that for the moment, I added a quick'n'dirty resolve_host()
function which should really go into netutils.c.  I just wanted to think
about its interface a bit more before providing such a function globally.

git-svn-id: https://nagiosplug.svn.sourceforge.net/svnroot/nagiosplug/nagiosplug/trunk@1766 f882894a-f735-0410-b71e-b25c423dba1c