The diff was incorrect. It was doing `diff -NIaupr`. And so diff was
interpreting the argument to -I to be `aupr`. So it was not running
recursively. The fix is not so simple because there is an intentionally
broken symlink in one of the godeps. Which diff -r fails on by default.
On linux there is an options to not dereference symlink and just make
sure they point to the same thing. No so on OS X. So we have to exclude
all files called "symlink". Which thankfully there is only one of.