Google test wrapper replaced by a lighter macro. This resolves #1577.

Now each unit test subdirectory has an identical copy of main.cpp,
and a file testlist.h that consists of #include's of all other .h
files in the subdirectory.
For the time being, the files testlist.h are not automatically
updated, but there is a script dev-tools/code-tools/update-gtestlist.py
that can be run when needed.