- use RbConfig for platform detection now.
- File.expand_path("/....") on windows platform returns "C:/...." which
is expected but not in our monkeypatching to work around other bugs.

  This should resolve logstash's known windows 'file input' problems and
  whatnot. I've tested this on a Windows Server 2012 EC2 instance
  provided by the Alex Corley at Zenoss <3

  Test config showed file inputs working. I was able to watch
  "C:\test.log" and edit the file with notepad, adding lines, and
  logstash would see new events show up when I saved.
- only bring in prctl if we're on linux
- one less use of Addressable::URI
Merge pull request #464 from jordansissel/fix-windows-file-problems

This PR should address: - https://logstash.jira.com/browse/LOGSTASH-430 It probably addresses other windows problems, but I couldn't find anything obvious in Jira.