Bug in hist_allow_clobber

[Wayne Davison <wayne@xxxxxxxxxxxxxxxxx>]

The code for option HIST_ALLOW_CLOBBER works well for '>', but it is
completely backward for '>>'.  Appended redirection gets the same
treatment as normal redirection, but what we really need is the
opposite:  It should turn ">>|file" into ">>file" and leave ">>file"
alone.

I also have a feature request:  When typing ">file" I often press TAB
(complete) to see if the file exists.  It would be nice in this case to
have the file expansion add the '|' to overwrite the file since I can't
accidentally overwrite a file when I purposely completed the filename.
Perhaps it should be an option, but I think it is straight forward
enough to be the default.

..wayne..