fix race condition

* spec/mspec/lib/mspec/helpers/fs.rb (Object#mkdir_p): fix race
  condition when multi_exec.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58952 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/mspec/lib/mspec/helpers/fs.rb

@@ -17,11 +17,18 @@ class Object
     parts.each do |part|
       name = File.join name, part
 
-      if File.file? name
+      stat = File.stat name
+      if stat.file?
         raise ArgumentError, "path component of #{path} is a file"
       end
 
-      Dir.mkdir name unless File.directory? name
+      unless stat.directory?
+        begin
+          Dir.mkdir name
+        rescue Errno::EEXIST
+          raise unless File.directory? name
+        end
+      end
     end
   end