Hi,
damn, this new configue option --with-glversion fixed all the problems I had on my Matrox machine! (I didn't yet test the i915 laptop.) Using --with-glversion=1.5 not only lets Gem render again on newest Mesa/DRI, it also gets rid of the crash when closing the Gem window! So, thank you for supporting older and hardware with buggy GL2.0-drivers again.
Ciao