Windows: Prevent git from changing line endings on test files

The sample3.ref test file is plain ascii, which means that Git on
Windows will automatically convert the line endings from \n to \r\n.
This of course causes a test to fail.

Added a .gitattributes file that requires Git to treat *.ref files as
binary, so it won't convert line endings.

.gitattributes

@@ -0,0 +1,16 @@
+# Handle line endings automatically for files detected as text
+# and leave all files detected as binary untouched.
+* text=auto
+
+#
+# The above will handle all files NOT found below
+#
+
+# Files that should be left untouched (binary is macro for -text -diff)
+*.ref           binary
+
+#
+# Exclude files from exporting
+#
+.gitattributes  export-ignore
+.gitignore      export-ignore