addremove: warn when addremove fails to operate on a named path

It looks like a bad path is the only mode of failure for addremove.  This
warning is probably useful for the standalone command, but more important for
'commit -A'.  That command doesn't currently abort if the addremove fails, but
it will be made to do so prior to adding subrepo support, since not all subrepos
will support addremove.  We could just abort here, but it looks like addremove
has always silently ignored bad paths, except for the exit code.

mercurial/scmutil.py

@@ -721,9 +721,15 b' def addremove(repo, matcher, opts={}, dr'
         similarity = float(opts.get('similarity') or 0)
 
     rejected = []
-    m.bad = lambda x, y: rejected.append(x)
+    origbad = m.bad
+    def badfn(f, msg):
+        if f in m.files():
+            origbad(f, msg)
+        rejected.append(f)
 
+    m.bad = badfn
     added, unknown, deleted, removed, forgotten = _interestingfiles(repo, m)
+    m.bad = origbad
 
     unknownset = set(unknown + forgotten)
     toprint = unknownset.copy()

tests/test-addremove.t

@@ -22,6 +22,16 b''
   $ hg forget foo
   $ hg -v addremove
   adding foo
+  $ hg forget foo
+#if windows
+  $ hg -v addremove nonexistant
+  nonexistant: The system cannot find the file specified
+  [1]
+#else
+  $ hg -v addremove nonexistant
+  nonexistant: No such file or directory
+  [1]
+#endif
   $ cd ..
 
   $ hg init subdir