Add C API PyUnicode_FromOrdinal() which exposes unichr() at C level.

u'%c' will now raise a ValueError in case the argument is an
integer outside the valid range of Unicode code point ordinals.

Closes SF bug #593581.

Include/unicodeobject.h

@@ -517,6 +517,18 @@ extern DL_IMPORT(int) PyUnicode_AsWideChar(
 
 #endif
 
+/* --- Unicode ordinals --------------------------------------------------- */
+
+/* Create a Unicode Object from the given Unicode code point ordinal. 
+ 
+   The ordinal must be in range(0x10000) on narrow Python builds
+   (UCS2), and range(0x110000) on wide builds (UCS4). A ValueError is
+   raised in case it is not.
+
+*/
+
+extern DL_IMPORT(PyObject*) PyUnicode_FromOrdinal(int ordinal);
+
 /* === Builtin Codecs ===================================================== 
 
    Many of these APIs take two arguments encoding and errors. These