AucTex and master file and pdf mode

[Richard Riley]

It's not clear to me from the docs how to default to pdf mode for all
files.  I have no need for dvi and pdf is more flexible with graphics
inclusion (e.g I just use png and not eps).

e.g If I set to pdflatex mode in an include it should also do that for
the master file when I try to compile the include.

I would love to hear your setup details.