Be more precise about what we ignore to avoid accidentally ignoring things.

(... for example, we might want a directory named source/vendor at some point to differentiate theme-provided JS/etc from user-provided...)

.gitignore

@@ -2,18 +2,19 @@
 .DS_Store
 *.sw[mnop]
 *~
-.sass-cache
-.gist-cache
-.pygments-cache
-_deploy
-public
-sass.old
-source.old
-source/_stash
-source/stylesheets/screen.css
-source/javascripts/*.min.js
-source/images/icon-*.png
-vendor
+/.sass-cache
+/.gist-cache
+/.pygments-cache
+/_deploy
+/public
+/sass.old
+/source.old
+/source/_stash
+/source/stylesheets/screen.css
+/source/javascripts/*.min.js
+/source/images/icon-*.png
+/vendor
+/lib/vendor
 node_modules
 /.preview-mode
 /_config.yml