In some places it was assumed that PATH_MAX does not include a
terminating null character.
Increases PATH_MAX to 1024 to get in sync with NetBSD. Required some
rewriting in AVFS to keep memory usage low (the stack in use by a thread
is very small).
This patch imports the unmodified current version of NetBSD libc.
The NetBSD includes are in /nbsd_include, while the libc code itself is
split between lib/nbsd_libc and common/lib/libc.