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/papi/package.py

@@ -0,0 +1,35 @@
+from spack import *
+import os
+
+class Papi(Package):
+    """PAPI provides the tool designer and application engineer with a
+       consistent interface and methodology for use of the performance
+       counter hardware found in most major microprocessors. PAPI
+       enables software engineers to see, in near real time, the
+       relation between software performance and processor events.  In
+       addition Component PAPI provides access to a collection of
+       components that expose performance measurement opportunites
+       across the hardware and software stack."""
+    homepage = "http://icl.cs.utk.edu/papi/index.html"
+    url      = "http://icl.cs.utk.edu/projects/papi/downloads/papi-5.3.0.tar.gz"
+
+    version('5.3.0', '367961dd0ab426e5ae367c2713924ffb')
+
+    def install(self, spec, prefix):
+        os.chdir("src/")
+
+        configure_args=["--prefix=%s" % prefix]
+
+		# need to force consistency in the use of compilers
+        if spec.satisfies('%gcc'):
+            configure_args.append('CC=gcc')
+            configure_args.append('MPICH_CC=gcc')
+        if spec.satisfies('%intel'):
+            configure_args.append('CC=icc')
+            configure_args.append('MPICH_CC=icc')
+
+        configure(*configure_args)
+
+        make()
+        make("install")
+