1. A code failure proneness estimation system comprising: a processor; a code metrics calculator implemented at least in part by the processor and configured to accept a code set and to calculate selected code metrics based on the code set, wherein the code set embodies a current version of software; a code churn calculator implemented at least in part by the processor and configured to accept and to calculate from the code set and a baseline code set code churn metrics that indicate a degree of change in the code set relative to the baseline code set, wherein the baseline code set embodies a previous version of the software; a historical variant metric feedback (“HVMF”) calculator configured to accept the code set and the baseline code set and baseline data associated with the baseline code set and calculate an HVMF factor and classify the selected code metrics and the code churn metrics; and a statistical modeler implemented at least in part by the processor and configured to accept the selected code metrics and the code churn metrics, and to perform a logistical regression resulting in a code failure proneness probability.