Have tap listeners specify whether the "packet" routine requires

Have tap listeners specify whether the "packet" routine requires

	a protocol tree;

	the column values.

This includes stats-tree listeners.

Have the routines to build the packet list, and to retap packets, honor
those requirements.  This means that cf_retap_packets() no longer needs
an argument to specify whether to construct the column values or not, so
get rid of that argument.

This also means that there's no need for a tap to have a fake filter
to ensure that the protocol tree will be built, so don't set up a fake
"frame" filter.

While we're at it, clean up some cases where "no filter" was represented
as a null string rather than a null pointer.

Have a routine to return an indication of the number of tap listeners
with filters; use that rather than the global num_tap_filters.

Clean up some indentation and some gboolean vs. gint items.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@28645 f5534014-38df-0310-8fa8-9805f1628bb7