change .path.package() to path.package()

With 
> R.version.string
[1] "R Under development (unstable) (2013-02-26 r62077)"

I was getting a number of warnings like this when buidi/reloading a package in an RStudio project:
Warning messages:
1: '.path.package' is deprecated.
Use 'path.package' instead.
See help("Deprecated") 

I didn't get these warnings in plain old R, and my code doesn't call either function, so I thought the warnings were coming from RStudio. Here I've changed RStudio's code to use path.packages() instead of .path.packages(). 

Thanks.
Dan