Feature Request: Add Trace functionality

At the bottom of every nodelist, there is a notice about the PING flag which states:

Nodes flying this flag will adhere to the following functionality:
;S
;S         1) PING-function:
;S         """""""""""""""""
;S             If a message destined to "PING" arrives at its final destination
;S             and this final destination flies the "PING"-flag, then the
;S             receiving node will bounce the message back to the original
;S             sender clearly displaying all the original via-lines.
;S
;S             If a message destined to "PING" arrives at its final destination
;S             but this final destination does _not_ fly the "PING"-flag then the
;S             message may be deleted from the inbound-queue without further
;S             follow-up.
;S
;S         2) TRACE-function:
;S         """"""""""""""""""
;S             If a message destined to "PING" arrives at a node which flies
;S             the PING-flag but is merely passing-through to another destination
;S             then the in-transit node will notify the sender of this occurence
;S             and will forward the original mail unaltered towards its final
;S             destination.

SBBS Supports the PING functionality (around line 4000 of sbbs.c), but doesn't report back when it is a pass-through system (aka TRACE)

There has also been some discussion about separating the TRACE and PING functions. Support for that would be nice.