[Ns-commits] ns-3-dev: fix more dox warnings

[code@nsnam-code.ece.gatech.edu]

user: Mathieu Lacage <mathieu.lacage at sophia.inria.fr>
files: doc/main.txt src/core/assert.h src/core/callback.h src/core/debug.h
url: http://code.nsnam.org/ns-3-dev?cmd=changeset;node=badb0e35d4c4686c50b5adcd74efb5a6aa9acee9