update .gitattributes

text=binary doesn't work well for some patches.

.gitattributes

@@ -1,12 +1,13 @@
 # Default.
 *           text eol=lf
 
-# Patches.
-*.diff      text=binary
-*.patch     text=binary
-*.patch32   text=binary
-*.patch64   text=binary
-*.patch.*   text=binary
+# Treat patch files as binaries but let diff'ing them
+# as normal text.
+*.diff      binary diff
+*.patch     binary diff
+*.patch32   binary diff
+*.patch64   binary diff
+*.patch.*   binary diff
 
 # Powershell scripts.
 *.ps1       text eol=crlf