windows: quote the specified string only when it has to be quoted Before this patch, "windows.shellquote" (as used as "util.shellquote") always quotes specified strings with double quotation marks, for external process invocation. But some problematic applications can't work correctly, when command line arguments are quoted: see issue4463 for detail. On the other hand, quoting itself is needed to specify arguments containing whitespaces and/or some special characters exactly. This patch makes "windows.shellquote" examine the specified string and quote it only when it may have to be quoted for safety.