only one ancestor or remote fits; a '^' means all of the ancestors
must be the same.
-case ancest head remote result
-----------------------------------------
-1 (empty)+ (empty) (empty) (empty)
-2ALT (empty)+ *empty* remote remote
-2 (empty)^ (empty) remote no merge
-3ALT (empty)+ head *empty* head
-3 (empty)^ head (empty) no merge
-4 (empty)^ head remote no merge
-5ALT * head head head
-6 ancest+ (empty) (empty) no merge
-8 ancest^ (empty) ancest no merge
-7 ancest+ (empty) remote no merge
-10 ancest^ ancest (empty) no merge
-9 ancest+ head (empty) no merge
-16 anc1/anc2 anc1 anc2 no merge
-13 ancest+ head ancest head
-14 ancest+ ancest remote remote
-11 ancest+ head remote no merge
+ case ancest head remote result
+ ----------------------------------------
+ 1 (empty)+ (empty) (empty) (empty)
+ 2ALT (empty)+ *empty* remote remote
+ 2 (empty)^ (empty) remote no merge
+ 3ALT (empty)+ head *empty* head
+ 3 (empty)^ head (empty) no merge
+ 4 (empty)^ head remote no merge
+ 5ALT * head head head
+ 6 ancest+ (empty) (empty) no merge
+ 8 ancest^ (empty) ancest no merge
+ 7 ancest+ (empty) remote no merge
+ 10 ancest^ ancest (empty) no merge
+ 9 ancest+ head (empty) no merge
+ 16 anc1/anc2 anc1 anc2 no merge
+ 13 ancest+ head ancest head
+ 14 ancest+ ancest remote remote
+ 11 ancest+ head remote no merge
Only #2ALT and #3ALT use *empty*, because these are the only cases
where there can be conflicts that didn't exist before. Note that we