If running multiple parallel processes of "xor_testfile.py" there was a
race condition between checking for the existence of the directory and
creating it. Now this is handled as a dependency in CMake.
The split test files are flagged by some AV's because they look like
broken executables. Instead of splitting the test files to prevent
detections, we should encrypt them. This commit replaces the "reassemble
testfiles" script with a basic "XOR testfiles" script that can be used
to encrypt or decrypt test files. This commit also of course then
replaces all the split files with xor'ed files.
The test and unit_tests directories were a bit of a mess, so I
reorganized them all into unit_tests with all of the test files placed
under "unit_tests/input" using subdirectories for different types of files.
