v2.6.8 - Fix for issue #558

[Kyle]

The big one here is a fix for bug 558 found by user @byunghyunna2. The largest changes were actually in the PCCC PLC code. Please test well. All my tests pass, but I cannot cover all users' scenarios.

There are other fixes for building with Debug and sanitizers on. That doesn't work, so the CMake config now prevents that.

Thanks to user CedricM for providing a test for parallel updates against the PLC simulator.

The release can be found here.

Best,

Kyle