Added a script to validate our .gitignore.

scripts/check-gitignore.sh

+#!/bin/bash
+
+## files we might want to ignore
+git ls-files -o --exclude-standard | sed -e "s:.:\/\\0:"
+
+## files we are accidentally ignoring
+git ls-files -i --exclude-standard | sed -e "s:.:\!\/\\0:"
+