The python_termainal plugin no longer segfaults

[Edward K. Ream]

Chris George discovered the cause: importing rlcompleter.  This is likely an obscure python bug.

rlcompleter handles tab completion, which is hardly an essential feature of this plugin. 

The fix was a new top-level switch:

use_rlcompleter = False
    # A workaround for #1212: segfaults at startup when importing this file.
    # True: enable tab completion, at the risk of segfaults.

Segfaults, when they happen at all, happened while Leo started up.  If you want typing completion, you can set this switch to True and see what happens ;-)

This fixed #1212.

Edward