Add script for removing trailing whitespace

This solution was suggested by @akaihola, and it is from a gist by
@dpaluy.  Originally from stack exchange (see the script for a link to
the gist and the discussion).

Closes python#408.

misc/remove-eol-whitespace.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+# Remove trailing whitespace from all non-binary files in a git repo.
+
+# From https://gist.github.com/dpaluy/3690668; originally from here:
+# http://unix.stackexchange.com/questions/36233/how-to-skip-file-in-sed-if-it-contains-regex/36240#36240
+
+git grep -I --name-only -z -e '' | xargs -0 sed -i -e 's/[ \t]\+\(\r\?\)$/\1/'