Add some tests for packages with multiple virtual dependencies.

- Added mock `hypre` package, depends on `lapack` and `blas`.

- test cases where some packages provide both `lapack` and `blas`, but
  others do not.

var/spack/repos/builtin.mock/packages/hypre/package.py

@@ -0,0 +1,39 @@
+##############################################################################
+# Copyright (c) 2013-2015, Lawrence Livermore National Security, LLC.
+# Produced at the Lawrence Livermore National Laboratory.
+#
+# This file is part of Spack.
+# Written by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
+# LLNL-CODE-647188
+#
+# For details, see https://github.com/llnl/spack
+# Please also see the LICENSE file for our notice and the LGPL.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License (as published by
+# the Free Software Foundation) version 2.1 dated February 1999.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the terms and
+# conditions of the GNU General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this program; if not, write to the Free Software Foundation,
+# Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+##############################################################################
+from spack import *
+
+class Hypre(Package):
+    """Hypre is included here as an example of a package that depends on
+       both LAPACK and BLAS."""
+    homepage = "http://www.openblas.net"
+    url      = "http://github.com/xianyi/OpenBLAS/archive/v0.2.15.tar.gz"
+
+    version('0.2.15', 'b1190f3d3471685f17cfd1ec1d252ac9')
+
+    depends_on('lapack')
+    depends_on('blas')
+
+    def install(self, spec, prefix):
+        pass

var/spack/repos/builtin.mock/packages/openblas-with-lapack/package.py

@@ -0,0 +1,38 @@
+##############################################################################
+# Copyright (c) 2013-2015, Lawrence Livermore National Security, LLC.
+# Produced at the Lawrence Livermore National Laboratory.
+#
+# This file is part of Spack.
+# Written by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
+# LLNL-CODE-647188
+#
+# For details, see https://github.com/llnl/spack
+# Please also see the LICENSE file for our notice and the LGPL.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License (as published by
+# the Free Software Foundation) version 2.1 dated February 1999.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the terms and
+# conditions of the GNU General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this program; if not, write to the Free Software Foundation,
+# Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+##############################################################################
+from spack import *
+
+class OpenblasWithLapack(Package):
+    """Dummy version of OpenBLAS that also provides LAPACK, for testing."""
+    homepage = "http://www.openblas.net"
+    url      = "http://github.com/xianyi/OpenBLAS/archive/v0.2.15.tar.gz"
+
+    version('0.2.15', 'b1190f3d3471685f17cfd1ec1d252ac9')
+
+    provides('lapack')
+    provides('blas')
+
+    def install(self, spec, prefix):
+        pass