[Xymon] Client startup on OS X

[Richard L. Hamilton]

> Thanks for the submits. The launch method used here is very similar to the
> that used on systemd systems, since they're both basically solving the
> same problem. This runclient support is coming in 4.4.
> 
> 
> The plist seems like something generic enough to include in the tarball,
> I'd think
> The macports version itself seems somewhat out of date:
> 
> https://trac.macports.org/browser/trunk/dports/net/xymon-client/Portfile
> 

I nudged on their list to get an update, given that the latest fixes some significant security issues; we'll see what happens.

You might want to at least clean up the environment variables in the plist file.  It may not be necessary to have them specified at all, but as a first attempt, I wanted something similar to starting it by hand.  At the very least, the PATH should be reduced to system default,  perhaps plus /sbin and /usr/sbin.

Mac account names can have aliases.  Non-human accounts often have the underscore prefix with an alias  without the underscore.  I think with the underscore is how MacPorts installed it, although I added the alias because other systems don't tend to have account names beginning with an underscore, and it's one less thing for my fingers to remember.  But it might look odd to some.

In the usual case, the umask (decimal equivalent of 022), and working directory, and capture of stdout/stderr might also be unnecessary.  As I said, I overspecified everything just to be sure it would work, esp. with any of my own scripts that might expect the usual environment; but the plist file would be less bother if it were minimized.  That would still leave pathnames, and account and group name, that could need changing depending on where and under what account/group someone installed Xymon.