add 'show threads' and 'show profile' commands.

add 'show threads' and 'show profile' commands.
These are momstly debugging tools for developers,
a bit documented in the header files (utils.h),
although more documentation is definitely necessary.

The performance impact is close to zero(*) so there is no
need to compile it conditionally.
(*) not completely true - thread destruction still needs
to search a list _but_ this can be easily optimized if we
end up with hundreds of active threads (in which case, though,
the problem is clearly elsewhere).

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@19544 65c4cc65-6c06-0410-ace0-fbb531ad65f3