Bin pointless '// predeclarations' or '// forward declarations' comments.  If
a programmer doesn't know what a forward declaration is, well, why read C++
source code?

Also bin some pointless '// end of namespace foo' comments after namespace
blocks just a handful of lines long, and some superfluous vertical whitespace.

Change-Id: I2a31c5d73d9b4de8825fb8eb9e7559dbd7303ef9