Add a CHANGELOG entry for the previous fix.
Fix --watch on Windows.

Closes #1409
Make sure the :filename option is consistently formatted.
Fix plugin test flakiness on Windows.
Fix more Windows tests.
Add a warning for too many varargs.

See #1408
Bump VERSION to 3.4.3.
adding appveyor configuration to this branch off stable
use a larger build matrix

new versions of Ruby (with DevKit) have been installed:
  - 1.9.3 x86 (C:\Ruby193 - default in PATH)
  - 2.0.0 x86 (C:\Ruby200)
  - 2.0.0 x64 (C:\Ruby200-x64)