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...)
Merge pull request #1060 from MrJoy/gitignore_cleanup_redux

Be more precise about what we ignore to avoid accidentally ignoring things.
Merge branch '2.1' of git://github.com/imathis/octopress into testing-2.1

Conflicts:
	.gitignore