copies: make it possible to distinguish betwen _computenonoverlap invocations _computenonoverlap needs to be invoked twice during a graft, and debugging messages should be distinguishable between the two invocations

copies: make _checkcopies handle simple renames in a rotated DAG This introduces a distinction between "merge base" and "topological common ancestor". During a regular merge, these two are identical. Graft, however, performs a merge in a rotated DAG, where the merge base will not be a common ancestor at all in the original DAG. To correctly find copies in case of a graft, we need to take both the merge base and the topological CA into account, and track any renames between them in reverse. Fortunately we can detect this in advance, see comment in the code about "backwards". This patch only supports finding non-divergent renames contained entirely between the merge base and the topological CA. Further patches are coming to support more complex cases. (Pierre-Yves David was involved in the cleanup of this patch.)

copies: compute a suitable TCA if base turns out to be unsuitable This will be used later in an update to _checkcopies. (Pierre-Yves David was involved in the cleanup of this patch.)

copies: detect graft-like merges Right now, nothing changes as a result of this, but we want to handle grafts differently from ordinary merges later. (Series developed together with Pierre-Yves David)

tests: introduce tests for grafting through renames These cover all currently known cases of renames being grafted, or changes being grafted through renames. Right now, most of these cases are broken. Later patches in this series will make them behave correctly. The testcases heavily rely on each other, which would make it very difficult to separate them and add them one-by-one for each case fixed by a patch. Separating them should perhaps be a 4.1 task, if it doesn't slow down the tests too much. (Developed together with Pierre-Yves David)

largefiles: fix 'deleted' files sometimes persistently appearing with R status A code snippet that has been around since largefiles was introduced was wrong: Standins no longer found in lfdirstate has *not* been removed - they have probably just been deleted ... or not created. This wrong reporting did that 'up -C' didn't undo the change and didn't sync the two dirstates. Instead of reporting such files as removed, propagate the deletion to the standin file and report the file as deleted.