Issue #173 Fix pipeline unit tests on Windows

- Switch to using filepath instead of path
- Add conditional tests for some error messages and filesytem permission checks
Issue #174 Fix sandbox unit test on Windows

- Account for the different return values of vsnprintf on Unix/Win
- Add our own sqrt function to work around the cgo link issue on Win
- Set *.data file attribute to eof=lf
Merge branch 'features/cmake' of github.com:mozilla-services/heka into features/cmake

Conflicts:
	pipeline/outputs.go
	pipeline/whisper.go