Ignore Sublime project files
Fix plugin loading paths for other OSs (eg. Windows)
Improve the absolute-path-checking code

* Fix the code, the absolute path condition was reversed!
* Improve absolute path detection: always check Unix separately
  because of the standard plugin load paths and the tests
* While at it, make it more similar to the rest
Streamline Windows path support code

* Add special assertion to compare paths
* Simplify test code by calling the new assertion
* Simplify a bit some path handling code
* This is more than anything to simplify Windows compatibility,
  but it should make path comparison more reliable, if anything
  (less spurious test failures)
Make sure tests using text fixtures work on Windows

* On Windows (depending on the Git client?), the fixtures get
  CRLF instead of just LF so the tests were failing
* Add new assertion to compare text that ignores CRLF/LF
  differences
Tiny code improvement in plugin load path handling