continue: added support for unshelve This patch adds the support for `ushelve` in `hg continue` plan. `hgcontinueunshelve()` has been created for independent calls. In case an interrupted unshelve is resumed via hg continue the shelvedstate needs to be loaded seperately. This has been ensured by `_loadunshelvedstate()` `hgcontinueunshelve()` is then registered as `continuefunc` for state detection API. Results are shown as tests. Differential Revision: https://phab.mercurial-scm.org/D6652