Fix off-by-one errors and increase PATH_MAX to 1024

Fix off-by-one errors and increase PATH_MAX to 1024

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).