revset: make follow() accept multiple startrevs The diff might look slightly complicated, but the initial "c = repo['.']" was effective if rev = None.

dagop: use heap to compute max rev in filectxancestors()

dagop: add smartset interface to filectxancestors() The original filectx API is kept public since we'll need it to walk ancestor (rev, match) pairs efficiently. The current implementation scans ancestors twice for 'hg log -fp FILE'.

overlayworkingctx: add `_checkexist(path)` This is in preparation to switch this class to inheriting (and being based off a) `commitctx` instead of a `workingctx`. `filectx` has no `exists` function, so this is how we'll fall back in that case. Differential Revision: https://phab.mercurial-scm.org/D1237

overlayworkingctx: fix a bad reference to `self._path` Differential Revision: https://phab.mercurial-scm.org/D1236

overlayworkingctx: track copy information in the context We can no longer do so in the dirstate, so add the functions to do so here. Differential Revision: https://phab.mercurial-scm.org/D1235

rebaseruntime: raise InMemoryMergeConflictsError on merge conflicts Differential Revision: https://phab.mercurial-scm.org/D1234

rebase: do not bail on uncomitted changes if rebasing in-memory Differential Revision: https://phab.mercurial-scm.org/D1233

rebase: add the --inmemory option flag; assign a wctx object for the rebase In the future, the --inmemory flag might be deprecated in favor of something more intelligent (for example, always rebasing in-memory if the working copy parent isn't in the rebaseset). But we might keep it as a way to explicitly force IMM on or off. Differential Revision: https://phab.mercurial-scm.org/D1232

overlayworkingctx: move _wrappedctx out of the constructor With rebase, we will be setting the _wrappedctx at a different point from the wctx construction (somewhat later, and possibly several times). Move it to a public function. Differential Revision: https://phab.mercurial-scm.org/D1231