Correct the RE equivalent of scanf()'s %x and %X patterns.

Closes SF bug #572169.

Doc/lib/libre.tex

@@ -862,7 +862,7 @@ offers some more-or-less equivalent mappings between
   \lineii{\code{\%u}}
          {\regexp{\e d+}}
   \lineii{\code{\%x}, \code{\%X}}
-         {\regexp{0[xX][\e dA-Fa-f]}}
+         {\regexp{0[xX][\e dA-Fa-f]+}}
 \end{tableii}
 
 To extract the filename and numbers from a string like