Another serie of fixes

Should fix #98 (closed) and also some return code from the command layer in lektord

inc/lektor/common.h

@@ -73,6 +73,9 @@ extern EXIT_FUNCTION ___not_implemented(const char *func, char *file, int line);
 /* For each, for flat-list. Need to be null terminated on the normally non-null field. */
 #define FOR_EACH_FLAT_LIST_ITEM(it, nnull_field) for (; (it)->nnull_field != NULL; it++)
 
+/* For each argument in a thing like a `char *args[]` */
+#define FOR_EACH_ARGUMENT(i, args) for (int i = 0; args[i]; ++i)
+
 /* Custom defined assert. */
 extern void (*___lkt_assert)(const char *file, int line, const char *func, const char *msg);
 #ifdef assert