context: make sure file is not deleted while checking path conflicts

If a file is deleted and a directory of same name is created in the same commit,
IMM thinks of that as a file conflict, however the file is deleted and hence the
directory can be created.

The test change demonstrate the fix.

Differential Revision: https://phab.mercurial-scm.org/D4300

mercurial/context.py

@@ -1896,7 +1896,7 b' class overlayworkingctx(committablectx):'
         components = path.split('/')
         for i in pycompat.xrange(len(components)):
             component = "/".join(components[0:i])
-            if component in self.p1():
+            if component in self.p1() and self._cache[component]['exists']:
                 fail(path, component)
 
         # Test the other direction -- that this path from p2 isn't a directory

tests/test-rebase-inmemory.t

@@ -177,8 +177,7 b' Test reporting of path conflicts'
   
   $ hg rebase -r . -d 2
   rebasing 4:daf7dfc139cb "a/a" (tip)
-  abort: error: 'a/a' conflicts with file 'a' in 2.
-  [255]
+  saved backup bundle to $TESTTMP/repo1/repo2/.hg/strip-backup/daf7dfc139cb-fdbfcf4f-rebase.hg
 
   $ cd ..