rebase: move local variables related to keeping things unchanged to the RR
This commit moves the following variables, local to the rebase function to be
fields of the rebaseruntime:
-keepf
-keepbranchesf
-keepopen
rebase: move local variables 'date' and 'extrafns' to the RR class
This commit moves the following variables, local to the rebase function to be
fields of the rebaseruntime:
-date
-extrafns