-Iextern/ => -Isrc/extern/

This was just a typo, it doesn't cause any problems for regular builds
because I have talloc, but it would cause a bug if for some reason
someone had pconfigure but not talloc.
Add PDFCOPY

Celio is providing me with raw PDF images that I can't do anything to
aside from copy into the directory (I guess I could crop them, but I
don't even want to touch them).

It turns out I've never had to do that before!