Closing a capture file has nothing to do with the list of interfaces on

Closing a capture file has nothing to do with the list of interfaces on
which to do a live capture; don't clear the latter list when closing the
capture file.

collect_ifaces() should clear out the existing list of interfaces before
filling that list up with the interfaces selected by the user.  In
addition, when it frees up interfaces in that list, it should free up
the strings attached to those interfaces.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@41517 f5534014-38df-0310-8fa8-9805f1628bb7