The trailing comma is supported in MPW and GCC. It fixes the formatting
issue with clang-format and makes cleaner diffs, so trailing commas have
been added to enums and clang-format has been run over the sources.
The main intent is to not allow enums to get condensed to a single line,
but this has the side effect of making clang-format stop attaching
braces to the start of the enum. I felt it made sense to use a different
brace style everywhere rather than live with just enums with braces on a
separate line.