libffi pull request builds on travis-ci have been failing for a while, but
now they are fixed.
At issue was the use of a travis-ci secret environment variable used as API
keys for https://rl.gl. As it happens, travis-ci doesn't allow the use of
these secret values in pull request builds -- only in the master and
feature branch builds. And so I implemented something called "policy bound
API keys" in rlgl. A policy bound API key is a key that can only be used
with a specific policy. So, in this case, I've bound
0LIBFFI-0LIBFFI-0LIBFFI-0LIBFFI to https://github.com/libffi/rlgl-policy.git.
This API key can be shared publicly, so now it is hard-coded in the
travis-ci build/test scripts, and used for every build.
The bottom line is that PR travis-ci tests are working again!