Utility to surround names of classes, etc with double quotes (not the single quotes of shQuote or the fancy quotes of dQuote)
the input string. Should be a name or something without quotes at least.
the string with quotes. But empty strings stay empty.
Chambers, John M. (2016) Extending R, Chapman & Hall/CRC. ( Chapter 12, discussing this package, is included in the package: ../doc/Chapter_XR.pdf.)