[SoM] Need a unit test for duplicate error codes.

[stephen-hawley]

The following shell command will print out the numbers that are duplicated for kCantHappenBase:
fgrep --include=\*.cs -rnw '/path/to/source' -e 'kCantHappenBase +' | grep -o "\+ \d\d*" | awk '{print $2}' | sort -n | uniq -d

This should run from either a unit test (ideal) or from the build.