Hi guilers!

This patch series defines:
* More AT_* and O_* flags.
* Bindings to *at functions (e.g. mkdirat, fchmodat).
* Bindings to f* functions (e.g. fchdir).
  (No new functions, the old functions just accept more types.)

It also sprinkles some scm_remember_upto_here's in
some procedures operating on ports where I think it's needed.

I haven't assigned copyright to the FSF, how would this work?

Greetings,
Maxime