Add a warning message when the user selects a BibTeX style that is not one of the standard 8.
Add a warning message when the user selects a BibTeX style that is not one of the standard 8.

JackieXie168/skim,JackieXie168/skim,JackieXie168/skim,JackieXie168/skim,JackieXie168/skim