2.6.0_alpha2 pulls in all the changes that went into 2.5.3 (some of which weren't in 2.6.0_alpha1), pulls in upstream changes from 1.9 RC6, and has a bunch of additional work on RandR which addresses the crash in alpha1 and better integrates RandR with the legacy rootless/fullscreen mode switching. It doesn't yet Capture/Release the screen like it should. I spent about 5 minutes working on that before the flight attendant made me turn off the laptop, and it was giving me issues, so it'll have to wait until next time.
You can just check for updates or grab it here:
http://static.macosforge.org/xquartz/downloads/SL/XQuartz-2.6.0_alpha2.dmg
Thanks,
Jeremy