Choose proper variable namings in tslib_cObj::getGlobal()
tslib_cObj::getGlobal() uses variable names like $c, $k, $a, $var, $vars etc
When working on #22392 and another patch (not yet registered in bugtracker) I struggled to find out how getGlobal() actually works. Proper naming of variables would be helpful.
(issue imported from #M14023)