Fix crlf issue with checkout tests

Move some checkout utility functions into a shared file and fix
some crlf filtering issues when verifying file contents.
Actually fix win32 checkout test

It turns out that using REMOVE_UNTRACKED with checkout for this
particular test was causing the .gitattributes file to be removed
and so we do have to allow for the CRs in the created file...
Merge pull request #1192 from arrbee/fix-win32-checkout-test

Fix win32 checkout test