append, prepend, cas

[dormando]

> 
> This issue is not addressed in the protocols document, so I wanted to
> know how these operators were thought out. I would think it would make
> more sense to have these operators extend and modify without having too
> specifying these arguments (and possibly add an update method to modify
> exptime and flags).
> 

Looked over the implementation of APPEND and PREPEND. It presently
overwrites the expiration time and flags using the new value.

I'd like to toss this back for a round on the list:

- Take the flags and exptime from 'old_item' before appending or
prepending the value and ignore what was sent.
- Only care about what was sent, leave things as they are.
- Dunno? Change them if nonzero?

Anyone care? Anyone planning on using append/prepend?

-Dormando