Composite Bypass Support Sharply Bumps XMir's Performance

Today's landing of the composite bypass support immediately increased the Intel Haswell graphic's performance by 14%. While a 14% performance improvement is significant (nearly an extra 30 frames per second for this setup), there's still another 5% improvement that's needed before it would be on par with the classic X.Org Server configuration.

The remainder of the OpenArena tests also demonstrated similar improvements where there's less of a performance regression in switching to Mir/XMir.