Fix SF bug 587012, doc mentions inexistent builtin unistr

Doc/api/abstract.tex

@@ -166,8 +166,8 @@ for which they do not apply, they will raise a Python exception.
   Compute a Unicode string representation of object \var{o}.  Returns
   the Unicode string representation on success, \NULL{} on failure.
   This is the equivalent of the Python expression
-  \samp{unistr(\var{o})}.  Called by the
-  \function{unistr()}\bifuncindex{unistr} built-in function.
+  \samp{unicode(\var{o})}.  Called by the
+  \function{unicode()}\bifuncindex{unicode} built-in function.
 \end{cfuncdesc}
 
 \begin{cfuncdesc}{int}{PyObject_IsInstance}{PyObject *inst, PyObject *cls}