lua-factory: warn on certain mistakes in the source table
lua-factory: warn on certain mistakes in the source table

This is a good way to pinpoint simple mistakes when creating the global
source table

https://bugzilla.gnome.org/show_bug.cgi?id=732879

jasuarez/grilo-plugins,grilofw/grilo-plugins,GNOME/grilo-plugins,grilofw/grilo-plugins,MikePetullo/grilo-plugins,MikePetullo/grilo-plugins,MikePetullo/grilo-plugins,GNOME/grilo-plugins,jasuarez/grilo-plugins