[medusa] support for sendfile() on linux and freebsd

[Sam Rushing]

I've added support for asynchronous sendfile() on linux and freebsd.

So now you can do something like this:

def my_method (self):
fd = os.open (filename, os.O_RDONLY, 0644)
size = os.lseek (fd, 0, 2)
os.lseek (fd, 0, 0)
self.push ('%08x' % size)
self.push_sendfile (fd, 0, size, self.close_that_descriptor)
self.close_when_done()

See the 'sendfile' subdirectory for details.

For you convenience, a new tarball has been rolled:

http://www.nightmare.com/medusa/medusa-src-20000201.tar.gz

Suggestions for a more portable interface are welcome, the current
setup is a bit clumsy.

Enjoy!

-Sam