title: fails to find cabal file when file present
body: <p>I have the following directory structure:
  <code>ls</code>: </p>
  
  <pre><code>  Project.Cabal
    LICENSE
    Setup.hs
    cabal.sandbox.config
    dist
    src
       Main.hs
       otherstuff
    tests
  </code></pre>
  
  <p>running <code>cabal install --only-denendencies</code> produces:
    cabal: Error reading local package.
    Couldn't find .cabal file in: .</p>
  
  <p>running <code>cabal install -v3 --only-dependencies</code> produces relatively lengthy output that I'm currently choosing not to post in full to avoid being immediatly overwhelming. The final few lines before error are:</p>
  
  <pre><code>The package database already exists:
  /Users/abraham/github/hamming_distance/.cabal-sandbox/x86_64-osx-ghc-7.10.2-packages.conf.d
  Reading available packages...
  Reading installed packages...
  ("/usr/bin/ghc-pkg",["dump","--package-db=/Users/abraham/github/hamming_distance/.cabal-sandbox/x86_64-osx-ghc-7.10.2-packages.conf.d","-v0"])
  ("/usr/bin/ghc",["--print-libdir"])
  Found no modified add-source deps.
  Reading installed packages...
  ("/usr/bin/ghc-pkg",["dump","--global","-v0"])
  ("/usr/bin/ghc-pkg",["dump","--package-db=/Users/abraham/github/hamming_distance/.cabal-sandbox/x86_64-osx-ghc-7.10.2-packages.conf.d","-v0"])
  ("/usr/bin/ghc",["--print-libdir"])
  Reading available packages...
  cabal: Error reading local package.
  Couldn't find .cabal file in: .
  </code></pre>
  
  <p>Similiarly, running <code>cabal build</code> produces:</p>
  
  <pre><code>Package has never been configured. Configuring with default flags. If this
  fails, please run configure manually.
  cabal: No cabal file found.
  Please create a package description file &lt;pkgname&gt;.cabal
  
  While running `cabal build -v3` produces:
  ..
  ..
  ..
  The package database already exists:
  /Users/abraham/github/hamming_distance/.cabal-sandbox/x86_64-osx-ghc-7.10.2-packages.conf.d
  Reading installed packages...
  ("/usr/bin/ghc-pkg",["dump","--global","-v0"])
  ("/usr/bin/ghc-pkg",["dump","--package-db=/Users/abraham/github/hamming_distance/.cabal-sandbox/x86_64-osx-ghc-7.10.2-packages.conf.d","-v0"])
  ("/usr/bin/ghc",["--print-libdir"])
  Reading available packages...
  cabal: No cabal file found.
  Please create a package description file &lt;pkgname&gt;.cabal
  </code></pre>
  
  <p>What is going on? Why is my cabal failing? And how do I fix it?</p>