R1:af295341c863

Classify changesets as "generated" at creation time, in addition to display time

Summary:
Ref T13130. See PHI251. Currently, changesets are marked as "generated" (i.e., the file contains generated code and does not normally need to be reviewed) at display time.

An install would like support for having Owners rules ignore generated files. Additionally, future changes anticipate making "generated" and some other similar behaviors more flexible and more general.

To support these, move toward a world where…