g_filename_display_basename() returns a g_mallocated string, so its

g_filename_display_basename() returns a g_mallocated string, so its
callers either need to free it or their callers need to free it or....

This means that cf_get_display_name() must always return a g_mallocated
string and its callers or... must free it.

For some of those callers, create a new set_window_title() routine to do
the work - they're all using the same pattern.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@43047 f5534014-38df-0310-8fa8-9805f1628bb7