memctx: calculate manifest correctly with newly-removed files (issue4470)

Before this patch, "memctx._manifest" tries to get (and use normally)
filectx also for newly-removed files, even though "memctx.filectx()"
returns None for such files.

To calculate manifest correctly even with newly-removed files, this
patch does:

  - replace "man.iteritems()" for the loop by "self._status.modified"
    to avoid accessing itself to newly removed files

    this also reduces loop cost for large manifest.

  - remove files in "self._status.removed" from the manifest

In this patch, amending is confirmed twice to examine both (1) newly
removed files and (2) ones already removed in amended revision.

mercurial/context.py

@@ -1649,6 +1649,10 b' class memctx(committablectx):'
         for f in self._status.added:
             man[f] = revlog.hash(self[f].data(), nullid, nullid)
 
+        for f in self._status.removed:
+            if f in man:
+                del man[f]
+
         return man
 
     @propertycache

tests/test-commit-amend.t

@@ -905,6 +905,58 b' Test that "diff()" in committemplate wor'
   HG: @@ -0,0 +1,1 @@
   HG: +y
 
+  $ hg rm a
+  $ HGEDITOR=cat hg commit --amend -e -m "expecting diff of a, foo and y"
+  expecting diff of a, foo and y
+  
+  HG: M: 
+  HG: A: foo y
+  HG: R: a
+  HG: diff -r 6de0c1bde1c8 a
+  HG: --- a/a	Thu Jan 01 00:00:00 1970 +0000
+  HG: +++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  HG: @@ -1,2 +0,0 @@
+  HG: -a
+  HG: -a
+  HG: diff -r 6de0c1bde1c8 foo
+  HG: --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  HG: +++ b/foo	Thu Jan 01 00:00:00 1970 +0000
+  HG: @@ -0,0 +1,1 @@
+  HG: +foo
+  HG: diff -r 6de0c1bde1c8 y
+  HG: --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  HG: +++ b/y	Thu Jan 01 00:00:00 1970 +0000
+  HG: @@ -0,0 +1,1 @@
+  HG: +y
+
+  $ hg rm x
+  $ HGEDITOR=cat hg commit --amend -e -m "expecting diff of a, foo, x and y"
+  expecting diff of a, foo, x and y
+  
+  HG: M: 
+  HG: A: foo y
+  HG: R: a x
+  HG: diff -r 6de0c1bde1c8 a
+  HG: --- a/a	Thu Jan 01 00:00:00 1970 +0000
+  HG: +++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  HG: @@ -1,2 +0,0 @@
+  HG: -a
+  HG: -a
+  HG: diff -r 6de0c1bde1c8 foo
+  HG: --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  HG: +++ b/foo	Thu Jan 01 00:00:00 1970 +0000
+  HG: @@ -0,0 +1,1 @@
+  HG: +foo
+  HG: diff -r 6de0c1bde1c8 x
+  HG: --- a/x	Thu Jan 01 00:00:00 1970 +0000
+  HG: +++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  HG: @@ -1,1 +0,0 @@
+  HG: -x
+  HG: diff -r 6de0c1bde1c8 y
+  HG: --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  HG: +++ b/y	Thu Jan 01 00:00:00 1970 +0000
+  HG: @@ -0,0 +1,1 @@
+  HG: +y
 
 Check for issue4405
 -------------------