add flag to recurse into subdirectories

Was wondering why this did not work. Fixes #58
Yes sorry, I meant relative paths like if you are in the lint folder and do a <code>golint golint/</code> which results into <code>cannot find package "golint" in any of: ...</code> with just importPaths. Don't know why I did not used that example. Or if you do a <code>golint golint/...</code> which results into <code>warning: "golint/..." matched no packages</code>.