icasefs: ignore removed files at building "dirstate._foldmap" up on icasefs

Before this patch, all files in dirstate are used to build "_foldmap"
up on case insensitive filesystem regardless of their statuses.

For example, when dirstate contains both removed file 'a' and added
file 'A', "_foldmap" may be updated finally by removed file 'a'. This
causes unexpected status information for added file 'A' at "hg status"
invocation.

This patch ignores removed files at building "_foldmap" up on case
insensitive filessytem.

This patch doesn't add any test, because this issue is difficult to
reproduce intentionally: it depends on iteration order of "dirstate._map".

mercurial/dirstate.py

@@ -59,7 +59,8 b' class dirstate(object):'
     @propertycache
     def _foldmap(self):
         f = {}
-        for name in self._map:
+        for name, s in self._map.iteritems():
+            if s[0] != 'r':
             f[util.normcase(name)] = name
         for name in self._dirs:
             f[util.normcase(name)] = name