./ns3 docs doxygen hides progress

./ns3 docs doxygen shows chatter from steps 0-3, but not step 4 (the actual doxygen build) which is the most time consuming.

The equivalent waf command (how fast I've forgotten!) did not suppress the doxygen chatter, so one had a way of gauging how long it was going to take, especially generating the figures.

There doesn't seem to be any way to turn this on with ./ns3 --verbose, and it doesn't appear to be piped to any file.