Relabeling cameras via python leads to different (worse) alignment

[dyoung]

Now that 1.6 is official, I won't waste my time comparing 1.5.5 to 1.6. But from some testing of 1.6, I can confirm that subdivide_task=True does seem to increase the processing time by 10-20% for at least some projects. However, it's really nice to have that option to reduce memory use for large projects.