Removing three references in Imports and NAMESPACE

Hi Yves, your package has made my life easier by including it in our package: http://cran.r-project.org/web/packages/NlsyLinks/index.html.  

I noticed R-Forge was griping that lavaan wasn't available (https://r-forge.r-project.org/R/?group_id=1330&log=build_src&pkg=NlsyLinks&flavor=patched).  I'm not sure why, because it's available for my Win8 and Ubuntu13.04 boxes without a problem.

Nevertheless, I came over here to see what could explain R-Forge's griping.  I didn't see any problems serious enough, but I thought I'd try to address some of the namespace and imports warnings that R CMD CHECK produced.  Depending on your setup, you probably don't care about the Rproj file and the two ignores.  R CMD CHECK had two other warnings that I mentioned in my first commit.

I hope this saves you more time than it costs you, and my feelings won't be hurt if they're ignored. -Will Beasley