daemon: allow more than one host address given via --listen

Hi, here is a new version of the two patches. The sockets are now in a socketlist structure that is compatible with ALLOC_GROW(). Also if no socket could be created for one host/ip, git daemon prints now an error but continues (in both ipv6 and noipv6 builds). Only if no socket could be created at all, it will die.

Also I removed the string_list_clear (it leave back memory leaks form the xstrdup'ed-strings). It would be happen just before the exit of the application and just before the operating system cleans the memory. So I hope, that it is okay to remove it. If not i will change it, to really free all lists before exit.

Thanks Alex