Fix encoding of \ in some string literals in the discussion of "raw"

strings.  Reported by Lorenzo M. Catucci <lorenzo@argon.roma2.infn.it>.

Doc/ref/ref2.tex

@@ -350,8 +350,8 @@ quote the following character, but \emph{all backslashes are left in
 the string}.  For example, the string literal \code{r"\e n"} consists
 of two characters: a backslash and a lowercase `n'.  String quotes can
 be escaped with a backslash, but the backslash remains in the string;
-for example, \code{r"\""} is a valid string literal consisting of two
-characters: a backslash and a double quote; \code{r"\"} is not a value
+for example, \code{r"\e""} is a valid string literal consisting of two
+characters: a backslash and a double quote; \code{r"\e"} is not a value
 string literal (even a raw string cannot end in an odd number of
 backslashes).  Specifically, \emph{a raw string cannot end in a single
 backslash} (since the backslash would escape the following quote