tiny autoconf2.50 patch for samba

[MCCALL,DON (HP-USA,ex1)]

Hi Martin,
Thought I would let you know that rsync is failing to
build on HP-UX 11.00 and 11.11  (using HP's ansi C compiler) because of a
test you have for socklen_t; on HP-UX 11.00 and 11.11, socklen_t is not
defined in types.h, but instead is defined in socket.h
Result is that we get socklen_t defined in config.h, and then get a complier
error when it gets REdefined in socket.h