Add URL parameter 'ignorews' for optionally ignoring whitespace in diffs

The new ctx.qry.ignorews variable is passed via cgit_diff_files() and
cgit_diff_tree() to Git's diff machinery. This is equivalent to passing
--ignore-all-space to 'git diff'.

Signed-off-by: Johan Herland <johan@herland.net>

cgit.c

@@ -252,6 +252,8 @@ static void querystring_cb(const char *name, const char *value)
 		ctx.qry.ssdiff = atoi(value);
 	} else if (!strcmp(name, "context")) {
 		ctx.qry.context = atoi(value);
+	} else if (!strcmp(name, "ignorews")) {
+		ctx.qry.ignorews = atoi(value);
 	}
 }