hgmerge: do not use file with markers in tools merging themselves
This time I forgot about a crucial part of the logic change.
The patch makes kdiff3 and tkdiff useful again.
Is there an error message when trying to diff non-existing files?
found: No such file or directory
not: No such file or directory
Is there an error message when trying to add non-existing files?
found: No such file or directory
not: No such file or directory