revert: add a test case to reverting "add" during merges

This kind of revert is specifically trickier since the file is
reported as "modified" by status. This case was only tested by some
largefiles test. We introduce proper testing of all aspects of this
case in the revert tests themselves.

tests/test-revert.t

@@ -299,4 +299,88 b' copies and renames, you have no chance t'
     removed
   R ignored
 
-  $ cd ..
+Test revert of a file added by one side of the merge
+
+(remove any pending change)
+
+  $ hg revert --all
+  forgetting allyour
+  forgetting base
+  undeleting ignored
+  $ hg purge --all --config extensions.purge=
+
+(Adds a new commit)
+
+  $ echo foo > newadd
+  $ hg add newadd
+  $ hg commit -m 'other adds'
+  created new head
+
+
+(merge it with the other head)
+
+  $ hg merge # merge 1 into 2
+  2 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ hg summary
+  parent: 2:b8ec310b2d4e tip
+   other adds
+  parent: 1:f6180deb8fbe 
+   rename
+  branch: default
+  commit: 2 modified, 1 removed (merge)
+  update: (current)
+
+(clarifies who added what)
+
+  $ hg status
+  M allyour
+  M base
+  R ignored
+  $ hg status --change 'p1()'
+  A newadd
+  $ hg status --change 'p2()'
+  A allyour
+  A base
+  R ignored
+
+(revert file added by p1() to p1() state)
+
+  $ hg revert -r 'p1()' 'glob:newad?'
+  $ hg status
+  M allyour
+  M base
+  R ignored
+
+(revert file added by p1() to p2() state)
+
+  $ hg revert -r 'p2()' 'glob:newad?'
+  removing newadd
+  $ hg status
+  M allyour
+  M base
+  R ignored
+  R newadd
+
+(revert file added by p2() to p2() state)
+spurious message comes from revert confusion when using p2. To be fixed soon.
+
+  $ hg revert -r 'p2()' 'glob:allyou?'
+  reverting allyour
+  $ hg status
+  M allyour
+  M base
+  R ignored
+  R newadd
+
+(revert file added by p2() to p1() state)
+
+  $ hg revert -r 'p1()' 'glob:allyou?'
+  removing allyour
+  $ hg status
+  M base
+  R allyour
+  R ignored
+  R newadd
+
+