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/trilinos/package.py

@@ -0,0 +1,50 @@
+from spack import *
+
+
+class Trilinos(Package):
+    """
+    The Trilinos Project is an effort to develop algorithms and enabling technologies within an object-oriented
+    software framework for the solution of large-scale, complex multi-physics engineering and scientific problems.
+    A unique design feature of Trilinos is its focus on packages.
+    """
+    homepage = "https://trilinos.org/"
+    url = "http://trilinos.csbsju.edu/download/files/trilinos-12.2.1-Source.tar.gz"
+
+    version('12.2.1', '6161926ea247863c690e927687f83be9')
+    version('12.0.1', 'bd99741d047471e127b8296b2ec08017')
+    version('11.14.3', '2f4f83f8333e4233c57d0f01c4b57426')
+    version('11.14.2', 'a43590cf896c677890d75bfe75bc6254')
+    version('11.14.1', '40febc57f76668be8b6a77b7607bb67f')
+
+    variant('mpi', default=True, description='Add a dependency on MPI and enables MPI dependent packages')
+
+    # Everything should be compiled with -fpic
+    depends_on('blas')
+    depends_on('lapack')
+    depends_on('boost')
+    depends_on('netcdf')
+    depends_on('matio')
+    depends_on('glm')
+    depends_on('swig')
+    depends_on('mpi', when='+mpi')
+
+    def install(self, spec, prefix):
+
+        options = [
+            '-DTrilinos_ENABLE_ALL_PACKAGES:BOOL=ON',
+            '-DTrilinos_ENABLE_TESTS:BOOL=OFF',
+            '-DTrilinos_ENABLE_EXAMPLES:BOOL=OFF',
+            '-DBUILD_SHARED_LIBS:BOOL=ON',
+            '-DBLAS_LIBRARY_DIRS:PATH=%s' % spec['blas'].prefix,
+            '-DLAPACK_LIBRARY_DIRS:PATH=%s' % spec['lapack'].prefix
+        ]
+        if '+mpi' in spec:
+            mpi_options = ['-DTPL_ENABLE_MPI:BOOL=ON']
+            options.extend(mpi_options)
+
+        # -DCMAKE_INSTALL_PREFIX and all the likes...
+        options.extend(std_cmake_args)
+        with working_dir('spack-build', create=True):
+            cmake('..', *options)
+            make()
+            make('install')