add a new cli/manager.conf option "debug" to enable/disable

add a new cli/manager.conf option "debug" to enable/disable
debugging code in the manager.
At the moment the debugging code is very lightweight, if the option
is enabled manager messages also carry a sequence number and
the info where they have been generated e.g.

SequenceNumber: 10
File: chan_sip.c
Line: 11927
Func: handle_response_register

It is not worthwhile having this as a compile time option
right now, because the extra work involved at runtime is
just checking one variable.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@47132 65c4cc65-6c06-0410-ace0-fbb531ad65f3