Git for Windows 1.9.4 changed the behavior when the text=auto
attribute is specified and core.autocrlf=false. Previous observed
behavior would *not* filter files when going into the working
directory, the new behavior *does* filter. Update our behavior to match.
When checking out files, we're performing conversion into the user's
native line endings, but we only want to do it for files which have
consistent line endings. Refuse to perform the conversion for mixed-EOL
files.
The CRLF->LF filter is left as-is, as that conversion is considered to be
normalization by git and should force a conversion of the line endings.
