Explicitly decode to UTF-8

Python 3 defaults to UTF-8 decoding, but Python 2 does not.  Also,
str.decode() on Python 2.6 doesn't accept keyword arguments.

Author: bgilbert

openslide/deepzoom.py

@@ -230,4 +230,4 @@ def get_dzi(self, format):
         tree = ElementTree(element=image)
         buf = BytesIO()
         tree.write(buf, encoding='UTF-8')
-        return buf.getvalue().decode()
+        return buf.getvalue().decode('UTF-8')

openslide/lowlevel.py

@@ -128,7 +128,7 @@ def _check_close(_result, _func, args):
 # Convert returned byte array, if present, into a string
 def _check_string(result, func, _args):
     if func.restype is c_char_p and result is not None:
-        return result.decode(errors='replace')
+        return result.decode('UTF-8', 'replace')
     else:
         return result
 
@@ -147,7 +147,7 @@ def _check_name_list(result, func, args):
         name = result[i]
         if not name:
             break
-        names.append(name.decode(errors='replace'))
+        names.append(name.decode('UTF-8', 'replace'))
     return names
 
 # resolve and return an OpenSlide function with the specified properties