[PATCH shelve-ext] shelve: make --keep option survive user intevention (issue5431)

[Mateusz Kwapich]

One less footgun in unshelve. Nice!

Excerpts from Kostia Balytskyi's message of 2016-11-23 10:51:47 -0800:
> diff --git a/hgext/shelve.py b/hgext/shelve.py
> --- a/hgext/shelve.py
> +++ b/hgext/shelve.py
> @@ -782,6 +787,7 @@ def _dounshelve(ui, repo, *shelved, **op
>  
>          try:
>              state = shelvedstate.load(repo)
> +            opts['keep'] = opts.get('keep') or state.keep
>          except IOError as err:
>              if err.errno != errno.ENOENT:
>                  raise
Respecting the "hg unshelve --continue --keep" while ignoring the
"hg unshelve --continue --no-keep" seems confusing to me. Either
we should always respoect the options provided to continue or we
should make them invalid.

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