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/gasnet/package.py

@@ -0,0 +1,35 @@
+from spack import *
+
+class Gasnet(Package):
+    """GASNet is a language-independent, low-level networking layer
+       that provides network-independent, high-performance communication
+       primitives tailored for implementing parallel global address space
+       SPMD languages and libraries such as UPC, Co-Array Fortran, SHMEM,
+       Cray Chapel, and Titanium.
+    """
+    homepage = "http://gasnet.lbl.gov"
+    url      = "http://gasnet.lbl.gov/GASNet-1.24.0.tar.gz"
+
+    version('1.24.0', 'c8afdf48381e8b5a7340bdb32ca0f41a')
+
+
+    def install(self, spec, prefix):
+        # TODO: don't use paths with @ in them.
+        change_sed_delimiter('@', ';', 'configure')
+
+        configure("--prefix=%s" % prefix,
+                  # TODO: factor IB suport out into architecture description.
+                  "--enable-ibv",
+                  "--enable-udp",
+                  "--disable-mpi",
+                  "--enable-par",
+                  "--enable-mpi-compat",
+                  "--enable-segment-fast",
+                  "--disable-aligned-segments",
+                  # TODO: make an option so that Legion can request builds with/without this.
+                  # See the Legion webpage for details on when to/not to use.
+                  "--disable-pshm",
+                  "--with-segment-mmap-max=64MB")
+
+        make()
+        make("install")