Check `$this` is instance of Config in get()
Check `$this` is instance of Config in get()

Check that `$this` is instance of `Concrete5_Model_Config` in
`Config::get()`

Because `Config::get()` is not declared static but is called statically,
it will inherit `$this` from the calling class.

If that class happens to have a `$pkg` property that is an object, we
will actually call `getPackageID()` on that object


Former-commit-id: 14317e5cfe40b0057f35fd9803fdec50e4798fa6
acliss19xx/concrete5,rikzuiderlicht/concrete5,rikzuiderlicht/concrete5,concrete5/concrete5,deek87/concrete5,biplobice/concrete5,hissy/concrete5,triplei/concrete5-8,biplobice/concrete5,mlocati/concrete5,KorvinSzanto/concrete5,MrKarlDilkington/concrete5,mainio/concrete5,KorvinSzanto/concrete5,hissy/concrete5,hissy/concrete5,rikzuiderlicht/concrete5,jaromirdalecky/concrete5,a3020/concrete5,concrete5/concrete5,jaromirdalecky/concrete5,MrKarlDilkington/concrete5,jaromirdalecky/concrete5,concrete5/concrete5,haeflimi/concrete5,deek87/concrete5,mlocati/concrete5,concrete5/concrete5,a3020/concrete5,mlocati/concrete5,olsgreen/concrete5,mainio/concrete5,triplei/concrete5-8,MrKarlDilkington/concrete5,triplei/concrete5-8,biplobice/concrete5,biplobice/concrete5,deek87/concrete5,hissy/concrete5,olsgreen/concrete5,mlocati/concrete5,KorvinSzanto/concrete5,acliss19xx/concrete5,deek87/concrete5,jaromirdalecky/concrete5,haeflimi/concrete5,haeflimi/concrete5,olsgreen/concrete5,haeflimi/concrete5,mainio/concrete5,acliss19xx/concrete5