In testing variable fw/precision in PR_Sprintf, I got a nasty reminder
of the limitations of the current progs ABI: passing @args to another QC
function does not work because the args list gets trampled but the
called function's locals. Thus, the need for a va_copy. It's not quite
the same as C's as it returns the destination args instead of copying
like memcpy, but it does copy the list from the source args to a
temporary buffer that is freed when the calling function returns.
Other than its blocking of access to certain files, it really wasn't
that useful compared to the functions in qfs, and pointless with access
to qfs anyway.
The api hides all the gory details of message buffer setup and usage
(particularly the differences between writing and reading). Most
importantly, the api provides a safe way to read and write binary data
(always little endian).
