Refactor Installer class into separate install and update processes

- Introduce separate Lock and LocalRepo transactions, one for changes
  to the lock file, one for changes to locally installed packages based
  on lock file
- Remove various hacks to keep dev dependencies updated and
  incorporated the functionality into the transaction classes
- Remove installed repo, there are now local repo, locked repo and
  platform repo
- Remove access to local repo from solver, only supply locked packages
- Update can now be run to modify the lock file but not install packages
  to local repo

tests/Composer/Test/DependencyResolver/SolverTest.php

@@ -30,6 +30,7 @@ class SolverTest extends TestCase
     protected $repoSet;
     protected $repo;
     protected $repoInstalled;
+    protected $repoLocked;
     protected $request;
     protected $policy;
     protected $solver;
@@ -39,6 +40,7 @@ class SolverTest extends TestCase
         $this->repoSet = new RepositorySet(array());
         $this->repo = new ArrayRepository;
         $this->repoInstalled = new InstalledArrayRepository;
+        $this->repoLocked = new ArrayRepository;
 
         $this->request = new Request($this->repoSet);
         $this->policy = new DefaultPolicy;
@@ -59,6 +61,7 @@ class SolverTest extends TestCase
     public function testSolverRemoveIfNotInstalled()
     {
         $this->repoInstalled->addPackage($packageA = $this->getPackage('A', '1.0'));
+        $this->repoLocked->addPackage(clone $packageA);
         $this->reposComplete();
 
         $this->checkSolverResult(array(
@@ -919,8 +922,8 @@ class SolverTest extends TestCase
 
     protected function reposComplete()
     {
-        $this->repoSet->addRepository($this->repoInstalled);
         $this->repoSet->addRepository($this->repo);
+        $this->repoSet->addRepository($this->repoLocked);
     }
 
     protected function createSolver()