(Try3) wininet/tests: Fix HttpSendRequestW test on IE5.

[Nicolas Le Cam]

Try3: Get back to original patch, change comment to indicate IE5
behavior, not Win2k to follow Hans comment.
Try2: Implement my remark as I didn't get any feedback.

Win2k SP4 seems to be the only platform that follows what msdn says (see
http://msdn.microsoft.com/en-us/library/aa384247(VS.85).aspx).

Perhaps passing header's length to HttpSendRequest instead of adding a
broken expected value would be better. Let me know.

--
Nicolas Le Cam