HCatalog is part of the Hive tarball but wasn't installed. The specific `HCAT_HOME` path (`/usr/local/Cellar/hive/0.12.0/libexec/hcatalog`) is Homebrew-specific the same way `HIVE_HOME` is 3 rows up.

Pig would not find HCatalog without this export because it looks for `/usr/lib/hcatalog` by default which is now obsolete.

All of this only applies if Pig is launched with the `-useHCatalog` switch. See: https://gist.github.com/rgabo/8375487