fix a typo in PyErr_Format table and add row for 'p' format char

closes bug 534495

Doc/api/exceptions.tex

@@ -139,7 +139,8 @@ for each thread.
     \lineii{c}{Character, as an \ctype{int} parameter}
     \lineii{d}{Number in decimal, as an \ctype{int} parameter}
     \lineii{x}{Number in hexadecimal, as an \ctype{int} parameter}
-    \lineii{x}{A string, as a \ctype{char *} parameter}
+    \lineii{s}{A string, as a \ctype{char *} parameter}
+    \lineii{p}{A hex pointer, as a \ctype{void *} parameter}
   \end{tableii}
 
   An unrecognized format character causes all the rest of the format