E.g. defining a `Foo::RED` enum name when a `GLOBAL::RED` identifier
already exists would previously be treated as an error, even though the
names don't truly conflict.
This also installs symlinks from "zeek" and "bro-config" to a wrapper
script that prints a deprecation warning.
The btests pass, but this is still WIP. broctl renaming is still
missing.
#239