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.

Furthermore, gtest.h included only in main.cpp, not in every single test (=> only tiny speed gain).

sort functions in MathFunctions;
rename 'value' -> 'x' or 'z'.

hacking in two standard formulae, Mr. Bond.

ParticleComposition