cgit.c: always setup cgit repo environment variables

When cgit learned to setup environment variables for certain repo
settings before invoking a filter process, the setup occurred inside
cgit_open_filter().

This patch moves the setup out of cgit_open_filter() and into
prepare_repo_cmd() to prepare for additional uses of these variables.

Reviewed-by: Ferry Huberts <mailings@hupie.com>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

ui-summary.c

@@ -113,7 +113,7 @@ void cgit_print_repo_readme(char *path)
 	 */
 	html("<div id='summary'>");
 	if (ctx.repo->about_filter)
-		cgit_open_filter(ctx.repo->about_filter, ctx.repo);
+		cgit_open_filter(ctx.repo->about_filter);
 	if (ref)
 		cgit_print_file(tmp, ref);
 	else