test-merge-changedelete.t: add a file with regular merge conflicts In upcoming patches we're going to move change/delete conflicts to the resolve phase -- it will be important to see how regular conflicts interact with change/delete ones.

filemerge: in ':prompt', use ':fail' tool rather than returning directly The ':fail' tool now knows to write out the changed side for change/delete conflicts. This has no impact right now but will make things better when we move change/delete conflicts in here.

filemerge: in ':fail' tool, write out other side if local side is deleted We do this because we don't want to modify the dirstate for failures, and don't just want to leave the file missing from disk. Plus it's more useful for the user if the changed side is written out -- it is easier to delete a file than to get it back via hg revert.