[PATCH] Fix util._statfiles_clustered() failing at root of a windows drive

[Andrei Vermel]

> What problem does it solve ?
> 
Files like "x:\.hgignore" get None instead of stat on return from
_statfiles_clustered().

This manifests itself e.g in a following problem: qrefresh in a subdirectory
records files in x:\ as deleted.

M:\>hg init

M:\>echo qqq>qqq.txt

M:\>hg add
adding qqq.txt

M:\>hg ci -m 1

M:\>mkdir aaa

M:\>cd aaa

M:\aaa>echo bbb>bbb.txt

M:\aaa>hg add
adding bbb.txt

M:\aaa>hg qnew -f -m "bbb" bbb_patch

M:\aaa>cat m:/.hg/patches/bbb_patch
bbb
diff --git a/aaa/bbb.txt b/aaa/bbb.txt
new file mode 100644
--- /dev/null
+++ b/aaa/bbb.txt
@@ -0,0 +1,1 @@
+bbb

M:\aaa>hg stat

M:\aaa>hg qref

M:\aaa>cat m:/.hg/patches/bbb_patch
bbb

diff --git a/aaa/bbb.txt b/aaa/bbb.txt
new file mode 100644
--- /dev/null
+++ b/aaa/bbb.txt
@@ -0,0 +1,1 @@
+bbb
diff --git a/qqq.txt b/qqq.txt
deleted file mode 100644
--- a/qqq.txt
+++ /dev/null
@@ -1,1 +0,0 @@
-qqq

M:\aaa>