Added new BC test

Updated throughout to use the "temp_build_files" dir on the build drive rather than the "generated" directory in the fbf source tree.

Moved the generation of the release metadata entry for the MD5 zip outside of the parallel section, so it can't co-incide with the zipping of the binaries. Ensured that any errors generated when merging log files are not just hidden by putting them in the output file (which will render it not well-formed XML).

Replaced <available> check with an <uptodate> check, to greatly help people working on the FBF who want the file automatically regenerated according to the changes they have made.