optimisation flag -Os instead of -O3.

make sure each .vcxproj file is with its corresponding source code.

add set -e to the build-mingw scripts to catch possible regressions.

CppUnit is really too large for our needs, would require to be precompiled
for many platforms, in all combinations of debug and release modes, with
additional variants for libstdc++ versions. We replace it with our own
lightweight implementation, LolUnit. Good riddance.

accordingly.