Sparse fixes for http-fetch

Sparse fixes for http-fetch

This patch cleans out all sparse warnings from http-fetch.c

I'm a bit uncomfortable with adding extra #ifdefs to avoid either
'mixing declaration with code' or 'unused variable' warnings, but I
figured that since those functions are already littered with #ifdefs I
might just get away with it. Comments?

[jc: I adjusted Peter's patch to address uncomfortableness issues.]

Signed-off-by: Peter Hagervall <hager@cs.umu.se>
Signed-off-by: Junio C Hamano <junkio@cox.net>