sha1dc: use proper string functions on Python 2/3

PyString_FromStringAndSize doesn't exist on Python 3: we need
to use PyUnicode_FromStringAndSize.

The extension now compiles without warnings on Python 2 and 3.

Differential Revision: https://phab.mercurial-scm.org/D7878

mercurial/thirdparty/sha1dc/cext.c

@@ -95,7 +95,7 b' static PyObject *pysha1ctx_hexdigest(pys'
 		hexhash[i * 2] = hexdigit[hash[i] >> 4];
 		hexhash[i * 2 + 1] = hexdigit[hash[i] & 15];
 	}
-	return PyString_FromStringAndSize(hexhash, 40);
+	return PY23(PyString_FromStringAndSize, PyUnicode_FromStringAndSize)(hexhash, 40);
 }
 
 static PyTypeObject sha1ctxType;