improve has_terminal()

This commit improves the code of `has_terminal()`
to work properly on OSX, if no terminal is
configured, i.e. no terminal is available.
Under OSX an `OSError` will be raised, which
is now properly caught.

datalad/ui/utils.py

@@ -84,5 +84,5 @@ def has_terminal():
     try:
         open('/dev/tty', 'r').close()
         return True
-    except IOError as exc:
+    except (IOError, OSError):
         return False