rebase: preserve active bookmark when not at head (issue3813) Now that the working directory parent is preserved, we can preserve the active bookmark too.

rebase: preserve working directory parent (BC) Prior to this changeset, rebase always left the working directory as a parent of the last rebased changeset. The is dubious when, before the rebase, the working directory was not a parent of the tip most rebased changeset. With this changeset, we move the working directory back to its original parent. If the original parent was rebased, we use it's successors. This is a step toward solving issue3813 (rebase loses active bookmark if it's not on a head)

tests: prepare rebase test for wc parent preservation In the way to solving issue3813 we'll preserve the working directory parent after the rebase. Multiple rebases test expect the working directory parent to be tip after rebase. We patches them before the actual change to prevent confusion.