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/qthreads/package.py

@@ -0,0 +1,22 @@
+from spack import *
+
+class Qthreads(Package):
+    """The qthreads API is designed to make using large numbers of
+       threads convenient and easy, and to allow portable access to
+       threading constructs used in massively parallel shared memory
+       environments. The API maps well to both MTA-style threading and
+       PIM-style threading, and we provide an implementation of this
+       interface in both a standard SMP context as well as the SST
+       context. The qthreads API provides access to full/empty-bit
+       (FEB) semantics, where every word of memory can be marked
+       either full or empty, and a thread can wait for any word to
+       attain either state."""
+    homepage = "http://www.cs.sandia.gov/qthreads/"
+    url      = "https://qthreads.googlecode.com/files/qthread-1.10.tar.bz2"
+
+    version('1.10', '5af8c8bbe88c2a6d45361643780d1671')
+
+    def install(self, spec, prefix):
+        configure("--prefix=%s" % prefix)
+        make()
+        make("install")