The Trusty build environment comes with a pkg-config file for CUnit
which lacks a version number and has a syntax error. The build script
now calls scripts/fix-cunit.sh to create a fixed version of the
existing cunit.pc file and point the configure script to this file.
The pkgconfig specification for libcunit1-dev version 2.1-2 is
horribly broken. build.sh (invoked by the travis CI system,
see .travis.yml) now runs a new script fix-cunit.sh when TESTS is
set to 'yes'.