Solaris sendfile: correctly detect amount of data sent

Solaris sendfile: correctly detect amount of data sent

Original message:

   Solaris sendfile seems to fail when sending moderately large (<1GB)
   files. Not a 32/64 problem, but a buffer problem.

   Anyone else ever try this? It is definitely broken in http-server.c.

   It seems to be broken in the following way:

   When sendfile sends partial data (EAGAIN, would block), "res" is
   always -1, rather than the amount sent.

   Here's a patch that reads from the "offset" pointer instead to
   discover what was sent. This seems to work: