IK-constraint "flush_targets" function was causing segfaults on debug builds from certain MSVC compilers.
The cause of this, is that ct is freed in the SINGLETARGET_FLUSH_TARS macro already, but ct is accessed in the following line to get the next target (ct= ct->next). Caused by brecht's commit for the pole-target stuff for IK-constraint.
Now the SINGLETARGET_FLUSH_TARS macro, and the SINGLETARGETNS_FLUSH_TARS macro will correctly advance the location that ct points to.
1e45289f91