Fix travis failures in fileutils due to smarter tmpdir.

Travis started failing after we updated tmpdir to allow using a
world-writable dir if sticky bit is set. The bug that was exposed
lies in FileUtils.remove_entry_secure, where it attempts to open
the "." entry in the target directory primarily to stat, chmod,
and chown it. Because JVM cannot open a stream to a directory
entry, JRuby can't do it either, and because we started allowing
tmpdir to use sticky-bit world-writable dirs, this logic started
getting hit for Dir.mktmpdir's cleanup.

The fix was to directly stat, chown, and chmod the "." entry
rather than opening it as a file, since these operations end up
equivalent.

Note of clarification: this issue has always existed, but most
uses of remove_entry_secure were either already in secure dirs
(non-world-writable) or insecure dirs with no sticky bit (in
which case remove_entry_secure raises an error, correctly). It
only became apparent because of the recent tmpdir change.

lib/ruby/1.8/fileutils.rb

@@ -696,14 +696,15 @@ def remove_entry_secure(path, force = false)
     end
     # freeze tree root
     euid = Process.euid
-    File.open(fullpath + '/.') {|f|
-      unless fu_stat_identical_entry?(st, f.stat)
+    dot_file = fullpath + "/."
+    File.lstat(dot_file).tap {|fstat|
+      unless fu_stat_identical_entry?(st, fstat)
         # symlink (TOC-to-TOU attack?)
         File.unlink fullpath
         return
       end
-      f.chown euid, -1
-      f.chmod 0700
+      File.chown euid, -1, dot_file
+      File.chmod 0700, dot_file
       unless fu_stat_identical_entry?(st, File.lstat(fullpath))
         # TOC-to-TOU attack?
         File.unlink fullpath

lib/ruby/1.9/fileutils.rb

@@ -718,14 +718,15 @@ def remove_entry_secure(path, force = false)
     end
     # freeze tree root
     euid = Process.euid
-    File.open(fullpath + '/.') {|f|
-      unless fu_stat_identical_entry?(st, f.stat)
+    dot_file = fullpath + "/."
+    File.lstat(dot_file).tap {|fstat|
+      unless fu_stat_identical_entry?(st, fstat)
         # symlink (TOC-to-TOU attack?)
         File.unlink fullpath
         return
       end
-      f.chown euid, -1
-      f.chmod 0700
+      File.chown euid, -1, dot_file
+      File.chmod 0700, dot_file
       unless fu_stat_identical_entry?(st, File.lstat(fullpath))
         # TOC-to-TOU attack?
         File.unlink fullpath