CommandNotFound -- enabling and disabling

[ghost]

CommandNotFound can be quite useful if you want to find out where a program may
reside. However had, it can also be noisy sometimes.

My suggestion would be to add --enable and --disable switches to it, to allow a user
to specifically disable or enable the CommandNotFound functionality.

When it is invoked, it can also specifically tell the user how to do the revert command
again such as:

CommandNotFound --disable

"Commands that were not found in the shell no longer give any hints."
"If you wish to toggle/revert this functionality, use the --enable argument."

Or something like that.

Sorry for filing it here, I do not know where CommandNotFound resides (I am writing
this on my non-gobo machine right now).