RStudio calls Rcmd.exe under Windows now, and Rcmd.exe treats `-v;` as an argument (WAT!), so let's use the more portable && instead of ;
fixes rstudio/rmarkdown#205: Encoding() returns these possible values: bytes, latin1, unknown, and UTF-8, among which only UTF-8 is a valid encoding name for iconv(), so we try to re-encode from UTF-8 if it is present in Encoding(), otherwise we assume the character vector has the native encoding
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