[PATCH 0/5] stgit rebasing fixes

The following series stores a backup of the stack-base to detect when it is safe to rebase or not (by "stg rebase" or "stg pull" in fetch+rebase mode).

The final patch in the series is the one implementing this, but is not tested enough for 0.12.1.

The previous ones, however, may be good to have in 0.12.1. Especially the patch that adds tracking of the orig-base parameter, since that will make things safer for more people when the final patch gets shipped (if no orig-base is found, rebasing is currently done without checking, to stay backwards-compatible).