dirstate: fix restoration of "merged" state after a remove

Before this change, "merged" file that get removed and re-added later were
recorded as "from_p2" instead.

This came from 8fe74328f700, a 2014 changeset that start explicitly doing so
for reason I have not been able to fully grasp.  The graft test mentioned in
the description are still happy after this changeset.

So this changeset restore what seems to be the intended behavior. Restoring
information as it was before the removal.

Differential Revision: https://phab.mercurial-scm.org/D11429

mercurial/dirstate.py

@@ -734,7 +734,10 b' class dirstate(object):'
                 # (see `merged_removed` and `from_p2_removed`)
                 if entry.merged_removed or entry.from_p2_removed:
                     source = self._map.copymap.get(f)
-                    self._addpath(f, from_p2=True)
+                    if entry.merged_removed:
+                        self._addpath(f, merged=True)
+                    else:
+                        self._addpath(f, from_p2=True)
                     self._map.copymap.pop(f, None)
                     if source is not None:
                         self.copy(source, f)

tests/test-merge-remove.t

@@ -55,8 +55,8 b' Re-adding foo1 and bar:'
   adding foo1
 
   $ hg debugstate --no-dates
-  n   0         -2 unset               bar
-  n   0         -2 unset               foo1
+  m   0         -2 unset               bar
+  m   0         -2 unset               foo1
   copy: foo -> foo1
 
   $ hg st -qC
@@ -74,8 +74,8 b' Reverting foo1 and bar:'
   reverting foo1
 
   $ hg debugstate --no-dates
-  n   0         -2 unset               bar
-  n   0         -2 unset               foo1
+  m   0         -2 unset               bar
+  m   0         -2 unset               foo1
   copy: foo -> foo1
 
   $ hg st -qC