Handle missing FileNotFoundError

Might not really be necessary, since py27 triggers the ImportError
always already, but better to be safe.

py/_path/common.py

@@ -10,6 +10,12 @@
 # Moved from local.py.
 iswin32 = sys.platform == "win32" or (getattr(os, '_name', False) == 'nt')
 
+try:
+    # FileNotFoundError might happen in py34, and is not available with py27.
+    import_errors = (ImportError, FileNotFoundError)
+except NameError:
+    import_errors = (ImportError,)
+
 try:
     from os import fspath
 except ImportError:
@@ -35,9 +41,7 @@ def fspath(path):
                 raise
             try:
                 import pathlib
-            except ImportError:
-                pass
-            except FileNotFoundError:  # Might happen in py34.
+            except import_errors:
                 pass
             else:
                 if isinstance(path, pathlib.PurePath):