New, cleaner package repository structure.

Package repositories now look like this:

    top-level-dir/
        repo.yaml
        packages/
            libelf/
                package.py
            mpich/
                package.py
            ...

This leaves room at the top level for additional metadata, source,
per-repo configs, indexes, etc., and it makes it easy to see that
something is a spack repo (just look for repo.yaml and packages).

var/spack/repos/builtin/packages/vim/package.py

@@ -0,0 +1,83 @@
+from spack import *
+
+class Vim(Package):
+    """Vim is a highly configurable text editor built to enable efficient text
+    editing. It is an improved version of the vi editor distributed with most
+    UNIX systems.  Vim is often called a "programmer's editor," and so useful
+    for programming that many consider it an entire IDE. It's not just for
+    programmers, though. Vim is perfect for all kinds of text editing, from
+    composing email to editing configuration files.
+    """
+
+    homepage = "http://www.vim.org"
+    url      = "ftp://ftp.vim.org/pub/vim/unix/vim-7.4.tar.bz2"
+    list_url = "http://ftp.vim.org/pub/vim/unix/"
+
+    version('7.4',     '607e135c559be642f210094ad023dc65')
+    version('7.3',     '5b9510a17074e2b37d8bb38ae09edbf2')
+    version('7.2',     'f0901284b338e448bfd79ccca0041254')
+    version('7.1',     '44c6b4914f38d6f9aa959640b89da329')
+    version('7.0',     '4ca69757678272f718b1041c810d82d8')
+    version('6.4',     '774c14d93ce58674b3b2c880edd12d77')
+    version('6.3',     '821fda8f14d674346b87e3ef9cb96389')
+    version('6.2',     'c49d360bbd069d00e2a57804f2a123d9')
+    version('6.1.405', 'd220ff58f2c72ed606e6d0297c2f2a7c')
+    version('6.1',     '7fd0f915adc7c0dab89772884268b030')
+    version('6.0',     '9d9ca84d489af6b3f54639dd97af3774')
+
+    feature_sets = ('huge', 'big', 'normal', 'small', 'tiny')
+    for fs in feature_sets:
+      variant(fs, default=False, description="Use '%s' feature set" % fs)
+
+    variant('python', default=False, description="build with Python")
+    depends_on('python', when='+python')
+
+    variant('ruby', default=False, description="build with Ruby")
+    depends_on('ruby', when='+ruby')
+
+    variant('cscope', default=False, description="build with cscope support")
+    depends_on('cscope', when='+cscope')
+
+    variant('gui', default=False, description="build with gui (gvim)")
+    # virtual dependency?
+
+    def install(self, spec, prefix):
+      feature_set = None
+      for fs in self.feature_sets:
+        if "+" + fs in spec:
+          if feature_set is not None:
+            tty.error("Only one feature set allowed, both %s and %s specified"
+                      % (feature_set, fs))
+          feature_set = fs
+      if '+gui' in spec:
+        if feature_set is not None:
+          if feature_set is not 'huge':
+            tty.error("+gui variant requires 'huge' feature set, %s was specified"
+                      % feature_set)
+        feature_set = 'huge'
+      if feature_set is None:
+        feature_set = 'normal'
+
+      configure_args = []
+      configure_args.append("--with-features=" + feature_set)
+
+      if '+python' in spec:
+        configure_args.append("--enable-pythoninterp=yes")
+      else:
+        configure_args.append("--enable-pythoninterp=dynamic")
+
+      if '+ruby' in spec:
+        configure_args.append("--enable-rubyinterp=yes")
+      else:
+        configure_args.append("--enable-rubyinterp=dynamic")
+
+      if '+gui' in spec:
+        configure_args.append("--enable-gui=auto")
+
+      if '+cscope' in spec:
+        configure_args.append("--enable-cscope")
+
+      configure("--prefix=%s" % prefix, *configure_args)
+
+      make()
+      make("install")