Advisory: Delete old libGL packages from poudriere repo before building new port vers

[Beeblebrox]

If you have your own poudriere repo and try to do a run based on a list of
upgraded packages only, you are likely to encounter several build errors
stating that
"libglapi conflicts with mesa-libs" or such.
To solve this either
a) Delete from your repo the packages: freeglut, libGL, libGLE, libglapi
b) Do a complete rebuild of all installed ports

The reason is that the poudriere run does not delete these packages on
startup, then tries to install both the new mesa-libs and the old libGL
packages that have not been deleted together in the same instance for
dependent port builds.

Hope this helps.