Rename _windows.h -> _win.h in system_wrappers.

- Also rename _dummy -> no_op which states its purpose more clearly.
- Always use exclusion lists (i.e. sources! instead of sources)

TEST=builds and passes system_wrapper_unittest on Linux, Mac, Win

Review URL: http://webrtc-codereview.appspot.com/317007

git-svn-id: http://webrtc.googlecode.com/svn/trunk@1199 4adac7df-926f-26a2-2b94-8c16560cd09d
30 files changed