cext: backout e9ca736f5b52 "remove Python 2 file handling code"

It's if"n"def.

mercurial/cext/osutil.c

@@ -1176,7 +1176,9 b' static PyObject *posixfile(PyObject *sel'
 	char fpmode[4];
 	int fppos = 0;
 	int plus;
+#ifndef IS_PY3K
 	FILE *fp;
+#endif
 
 	if (!PyArg_ParseTupleAndKeywords(args, kwds, "et|yi:posixfile",
 					 kwlist,
@@ -1248,6 +1250,7 b' static PyObject *posixfile(PyObject *sel'
 		PyErr_SetFromErrnoWithFilename(PyExc_IOError, name);
 		goto bail;
 	}
+#ifndef IS_PY3K
 	fp = _fdopen(fd, fpmode);
 	if (fp == NULL) {
 		_close(fd);
@@ -1262,6 +1265,11 b' static PyObject *posixfile(PyObject *sel'
 	}
 
 	PyFile_SetBufSize(file_obj, bufsize);
+#else
+	file_obj = PyFile_FromFd(fd, name, mode, bufsize, NULL, NULL, NULL, 1);
+	if (file_obj == NULL)
+		goto bail;
+#endif
 bail:
 	PyMem_Free(name);
 	return file_obj;