[Fab-user] Completed suggestions: prompt (#5, #6)

[Niklas Lindström]

[These changes are present in my fork of Fabric at
<http://github.com/niklasl/fabric/tree/master>]


== 5. Prompt, repeat and validate ==

`prompt` repeats if a validator (via `validate` keyword) throws
exception. The exception message is printed before repeat.

`prompt` also validates any variable already defined.

Opinions: I believe Christian is ok with this if Jeff approves of it?


== 6. Prompt, validate with regexp ==

If the `validate keyword of `prompt` is a string, it is turned into a
RegexpValidator instance (itself callable), which raises an exception
if the given value doesn't match.


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Best regards,
Niklas