[Hackage] #390: add cabal unpack command

[Hackage]

#390: add cabal unpack command
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  Reporter:  duncan              |        Owner:                 
      Type:  enhancement         |       Status:  new            
  Priority:  normal              |    Milestone:                 
 Component:  cabal-install tool  |      Version:                 
  Severity:  normal              |   Resolution:                 
  Keywords:                      |   Difficulty:  easy (<4 hours)
Ghcversion:  6.8.3               |     Platform:                 
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Comment (by Saizan):

 I've needed this command a lot lately, so i've written this patch.

 There are 2 TODOs there since i wasn't sure what was best from an UI pov:

 * When no precise version is specified it defaults to the latest that
 match,
   should we also take the packagePreferences field in consideration here?

 * Currently it ignores exceptions (however if something goes wrong the
 functions involved still print error messages), summarizing failures at
 the end like in 'cabal install' is probably what we want.

-- 
Ticket URL: <http://hackage.haskell.org/trac/hackage/ticket/390#comment:3>
Hackage <http://haskell.org/cabal/>
Hackage: Cabal and related projects