[Bug-AUCTeX] Bug detecting PDFLaTeX mode

[Mike Spertus]

If I have a master file which uses pdflatex, it is properly detected by 
the auctex parser when the master file is loaded and PDFLaTeX mode is 
enabled. However, if I have another document that uses the same document 
as it's TeX-master, it is opened in LaTeX mode, even though the exact 
same document should be built. I think the correct solution would be to 
scan the master file (at least if TeX-mode isn't set).

Thanks,

Mike