* bootstrap: Add stdio-safer, unistd-safer modules.

* bootstrap: Add stdio-safer, unistd-safer modules.
Remove m4/glibc2.m4 (introduced by latest gnulib, but
we don't need it).
* lib/.cvsignore: Add dup-safer.c, fd-safer.c,
fopen-safer.c, stdio-safer.h, unistd-safer.h.
* lib/subpipe.c: Include "unistd-safer.h".
(create_subpipe): Make sure all the newly-created
file descriptors are > 2, so that diagnostics don't
get sent down them (which might cause Bison to hang, in theory).
* m4/.cvsignore: Add stdio-safer.m4, unistd-safer.m4.
* src/files.c (xfopen): Use fopen_safer, not fopen.