tests: add test case for criss cross merge

The test do not fit in any existing test file...

tests/test-merge-criss-cross.t

@@ -0,0 +1,111
+Criss cross merging
+
+  $ hg init criss-cross
+  $ cd criss-cross
+  $ echo '0 base' > f1
+  $ echo '0 base' > f2
+  $ hg ci -Aqm '0 base'
+
+  $ echo '1 first change' > f1
+  $ hg ci -m '1 first change f1'
+
+  $ hg up -qr0
+  $ echo '2 first change' > f2
+  $ hg ci -qm '2 first change f2'
+
+  $ hg merge -qr 1
+  $ hg ci -m '3 merge'
+
+  $ hg up -qr2
+  $ hg merge -qr1
+  $ hg ci -qm '4 merge'
+
+  $ echo '5 second change' > f1
+  $ hg ci -m '5 second change f1'
+
+  $ hg up -qr3
+  $ echo '6 second change' > f2
+  $ hg ci -m '6 second change f2'
+
+  $ hg log -G
+  @  changeset:   6:3b08d01b0ab5
+  |  tag:         tip
+  |  parent:      3:cf89f02107e5
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     6 second change f2
+  |
+  | o  changeset:   5:adfe50279922
+  | |  user:        test
+  | |  date:        Thu Jan 01 00:00:00 1970 +0000
+  | |  summary:     5 second change f1
+  | |
+  | o    changeset:   4:7d3e55501ae6
+  | |\   parent:      2:40663881a6dd
+  | | |  parent:      1:0f6b37dbe527
+  | | |  user:        test
+  | | |  date:        Thu Jan 01 00:00:00 1970 +0000
+  | | |  summary:     4 merge
+  | | |
+  o---+  changeset:   3:cf89f02107e5
+  | | |  parent:      2:40663881a6dd
+  |/ /   parent:      1:0f6b37dbe527
+  | |    user:        test
+  | |    date:        Thu Jan 01 00:00:00 1970 +0000
+  | |    summary:     3 merge
+  | |
+  | o  changeset:   2:40663881a6dd
+  | |  parent:      0:40494bf2444c
+  | |  user:        test
+  | |  date:        Thu Jan 01 00:00:00 1970 +0000
+  | |  summary:     2 first change f2
+  | |
+  o |  changeset:   1:0f6b37dbe527
+  |/   user:        test
+  |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    summary:     1 first change f1
+  |
+  o  changeset:   0:40494bf2444c
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     summary:     0 base
+  
+
+  $ hg merge -v --debug --tool internal:dump 5
+    searching for copies back to rev 3
+  resolving manifests
+   branchmerge: True, force: False, partial: False
+   ancestor: 0f6b37dbe527, local: 3b08d01b0ab5+, remote: adfe50279922
+   f1: remote is newer -> g
+   f2: versions differ -> m
+    preserving f2 for resolve of f2
+  getting f1
+  updating: f1 1/2 files (50.00%)
+  updating: f2 2/2 files (100.00%)
+  picked tool 'internal:dump' for f2 (binary False symlink False)
+  merging f2
+  my f2@3b08d01b0ab5+ other f2@adfe50279922 ancestor f2@40494bf2444c
+  1 files updated, 0 files merged, 0 files removed, 1 files unresolved
+  use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
+  [1]
+
+  $ head *
+  ==> f1 <==
+  5 second change
+  
+  ==> f2 <==
+  6 second change
+  
+  ==> f2.base <==
+  0 base
+  
+  ==> f2.local <==
+  6 second change
+  
+  ==> f2.orig <==
+  6 second change
+  
+  ==> f2.other <==
+  2 first change
+
+  $ cd ..