some small Cython code improvements, thanks to Stefan Behnel

borg/hashindex.pyx

@@ -24,15 +24,18 @@ cdef extern from "_hashindex.c":
     int _le32toh(int v)
 
 
-_NoDefault = object()
+cdef _NoDefault = object()
 
+cimport cython
+
+@cython.internal
 cdef class IndexBase:
     cdef HashIndex *index
     key_size = 32
 
     def __cinit__(self, capacity=0, path=None):
         if path:
-            self.index = hashindex_read(<bytes>os.fsencode(path))
+            self.index = hashindex_read(os.fsencode(path))
             if not self.index:
                 raise Exception('hashindex_read failed')
         else:
@@ -49,7 +52,7 @@ cdef class IndexBase:
         return cls(path=path)
 
     def write(self, path):
-        if not hashindex_write(self.index, <bytes>os.fsencode(path)):
+        if not hashindex_write(self.index, os.fsencode(path)):
             raise Exception('hashindex_write failed')
 
     def clear(self):