Fix lots of compiler warnings

Mostly unused variables and parameters
.dir-locals.el: actually make it all work

Since I use dtrt-indent, I hadn't noticed this wasn't working at all;
sorry. Actually tested now.
configure.ac: fix some whitespace in generated config.h
parsepdf.c: fix a comment typo
psread.c: fix most compiler warnings
namelist.c: fix an annoying number of compiler warnings about const
Change some member names to avoid clashes with re-#defined symbols