graft: introduce --base option for using custom base revision while merging The graft command usually performs an internal merge of the current parent revision with the graft revision, using p1 of the grafted revision as base for the merge. As a trivial extension of this, we introduce the --base option to allow for using another base revision. This can be used as a building block for grafting and collapsing multiple changesets at once, or for grafting the resulting change from a merge as a single simple change. (This is kind of similar to backout --parent ... only different: this graft base must be an ancestor, but is usually *not* a parent.) This is probably an advanced use case, and we do thus not show it in the non-verbose help.

changegroup: add a option to create bundle with full snapshot only This is easy to implement now and can be useful for benchmarking.

changegroup: allow to force delta to be against p1 This new developer option is useful to general more "generic" bundle. Without this option, a bundle generated from the repository use deltas similar to the one stored in the specific repository it was generated from. This makes performance testing a bit tricky. Using deltas similar to the final result means all delta stored in the bundle can be applied to the target repository without any further processing (except for the rare case of a full snapshot). The application of such bundles (almost) never exercises the (slower) path of searching for a new valid delta. This result in unrealistic and too favorable timing and profile. Instead, we introduce an option to make sure all revisions are stored as a delta against p1. It might not be the best generation option, but it guarantees that the content will be "generic", not favoring a specific target.