当没有对默认库位置的读/写访问权限时，从自定义库位置加载R包

We use R at my university, where all computers run Windows XP or Windows 7 and read/write access to most places on the C drive is disabled. This includes the default directory for downloading and installing R packages, but does not include the Downloads folder, so I've been using this work-around:We use R at my university, where all computers