Small corrections to `@examples` in Rd vignette

* The wording was modified in a few places

* The only real correction was removing the `x` from the cell at the intersection of `\donttest{}` and `R CMD check`.  Please verify that I correctly interpreting http://cran.r-project.org/doc/manuals/R-exts.html#Documenting-functions.

* I didn't update the actual vignettes (just the Rmd source code), because I was getting errors during the build process.  I didn't think it was worth figuring out for this vignette, but tell me if you'd like more details.
Merge pull request #209 from wibeasley/patch-2

Small corrections to `@examples` in Rd vignette