re: #pragma once

[matthew green <mrg%eterna.com.au@localhost>]

i am a fan of #pragma once.  the main reason is that it avoids
the class of bugs where you copy a header and forget to change
the #define and then sometimes the header is empty upon use,
and you end up having to use cpp output to debug it.

i'd be ok with using it anywhere -- AFAIK the compiler support
is available everywhere.

note that it is already used in libpcap, bind, libuv, and as a
test for xlint, in our tree, for consumed components.


.mrg.