title: Cabal install failure on existing sandbox in Windows
body: <p>I have installed the Haskell-platform on Windows. I am trying to build an existing project from an existing cabal sandbox. Whenever I attempt to reinstall, all packages fail with the following error:</p>
  
  <pre><code>cabal.exe: expected an absolute directory name for --prefix:
  </code></pre>
  
  <p>Was wondering where I need to specify an absolute directoy. Cabal is installed here:
  Note: I am using <code>Powershell</code> to execute these commands.</p>
  
  <pre><code>C:\Users\user\AppData\Roaming\cabal\bin\cabal.exe
  </code></pre>
  
  <p>Here's the full output.</p>
  
  <pre><code>websockets-snap-0.8.2.1 (new package)
  Project-0.1 (new package)
  cabal.exe: The following packages are likely to be broken by the reinstalls:
  haskell-platform-2013.2.0.0
  cgi-3001.1.7.5
  Use --force-reinstalls if you want to install anyway.
  PS C:\Users\user\Project&gt; cabal install --force-reinstalls
  Resolving dependencies...
  Warning: The following packages are likely to be broken by the reinstalls:
  haskell-platform-2013.2.0.0
  cgi-3001.1.7.5
  Continuing even though the plan contains dangerous reinstalls.
  Configuring Crypto-4.2.5.1...
  cabal.exe: expected an absolute directory name for --prefix:
  /Users/user/Project/.cabal-sandbox
  Failed to install Crypto-4.2.5.1
  Configuring MonadRandom-0.1.13...
  cabal.exe: expected an absolute directory name for --prefix:
  /Users/user/Project/.cabal-sandbox
  Failed to install MonadRandom-0.1.13
  Configuring SHA-1.6.1...
  cabal.exe: expected an absolute directory name for --prefix:
  /Users/user/Project/.cabal-sandbox
  Failed to install SHA-1.6.1
  </code></pre>
  
  <p>How do I specify an absolute directory name for prefix?</p>