Unit tests. This is a set of unit tests in the making, but *far* from
complete. To run it,
- install CxxTest (version 3.9.1)
- invoke 'make CXXTESTDIR=/where/you/have/cxxtest testsuite'
- invoke './testsuite'

Note that the file-system based tests assume to be able to create some
files called 'nnXXXXXX.dat', where the first two characters (nn) are
digits, followed by six other characters. If the current directory is
not writable or full, or some such files exist prior to the test, the
tests might fail spuriously.
