[ns] debugging/verbose output in ns

[Haobo Yu <haoboy@isi.edu>]

Hi, 

Following a discussion of Mark Allman and Lloyd Wood long time ago, I
added a very simple function to TclObject to generate debugging/verbose
output. Essentially one may call function TclObject::debug() in the same
way as calling a printf(), but it only writes output when an otcl-bound
variable debug_ is true. In this way, one may turn on/off verbose outputs
for a particular object.

This has appeared in the daily snapshot. Work is under way to convert
existing printfs to this method. 

Your comments are welcome.

- Haobo