filemerge._mergecheck: add check for change/delete conflicts Merge tools that perform an actual 3-way merge can't handle change/delete conflicts. This adds a check for that.

filemerge._picktool: only pick from nomerge tools for change/delete conflicts For --tool or HGMERGE, we could have either: (a) proceeded with the particular tool, then failed the merge. (b) chosen to prompt regardless. We're explicitly choosing (b) here, because it's effectively what we've been doing so far and helps maintain an easier-to-use interface. However, in future patches we're going to change the default selection from 'pick changed version' to 'leave unresolved'. That fixes most of the brokenness involved with choice (b).

filemerge: add support for change/delete conflicts to the ':prompt' tool We haven't added the 'leave unresolved' option yet -- that will come in a future patch.

filemerge: add support for change/delete conflicts to the ':other' merge tool This, along with the previous patch to the :local merge tool, covers the full matrix of change/delete conflicts.

filemerge: add support for change/delete conflicts to the ':local' merge tool This covers two of the four cases of change/delete conflicts -- in an upcoming patch we'll make :other cover the other two.

merge.mergestate: compute dirstate action In upcoming patches we're going to queue these actions up to be applied to the dirstate at the end.

filemerge: return whether the file was deleted This is required for change/delete conflict resolution -- see previous patches for more details.

filemerge: return whether the file is deleted from all other merge tools This is required for change/delete conflicts -- see the previous patch for more information.

filemerge: return whether the file is deleted for nomerge internal tools We're going to support the filemerge code resolving change/delete conflicts in upcoming patches. Some of these resolutions require that the dirstate be modified. Modifying the dirstate directly from in here would be (a) a pretty bad layering violation and (b) wrong because all dirstate removals should happen before adds. So in this and upcoming patches we're instead going to pass whether the file is deleted up to merge.mergestate, then in there figure out what dirstate action needs to be taken.

mergestate: allow storing and retrieving change/delete conflicts We introduce a new record type, 'C', to indicate change/delete conflicts. This is a separate record type because older versions of Mercurial will not be able to handle these conflicts. We aren't actually storing any change/delete conflicts yet -- that will come in future patches.