add mpi4py from March 2014
Add Linux Arch environment and host packages

* Revision of 5c238

Suggested-by: Jed Brown <jed@jedbrown.org>
Closes #159 by making the cmake_package feature complete.

The cmake_package by default sets CMAKE_INSTALL_RPATH, and
CMAKE_INSTALL_RPATH_USE_LINK_PATH by default. It also uses the global
debug flag to determine the value for DCMAKE_BUILD_TYPE.

Also for CMake builds we need to setup CMAKE_PREFIX_PATH with the
directories of our dependencies, this allows CMake projects calls
to find_* to first look at hashdist build versions first.
Remove all redundant values from cmake packages.
Add a test to verify the new cmake package works.
Correct launcher to use the default compiler.

This allows launcher to be used on machines where gcc isn't the default
compiler.
Hand-merge .travis.yaml

Also noting (courtesy Robert Maynard)

> I didn't clearly state this in the commit message but by explicitly
adding a CMake variable to the extra section it will override any of the
values that cmake_package sets. This happens because CMake treats the
last occurrence of a value is the preferred one, and I make sure to add
the extra section last.
Add Clawpack + Git Submodule test

Clawpack uses relative submodules, so it's a good test of our submodule
functionality.  This does not test the parallel aspects of Clawpack, but
this could be added by installing a PETSc installation.
Merge pull request #183 from robertmaynard/cmake_package

Cmake package
Merge pull request #184 from robertmaynard/update_launcher

Correct launcher to use the default compiler.
Merge pull request #185 from hashdist/add_clawpack_test

Add Clawpack + Git Submodule test
Merge pull request #182 from hashdist/ahmadia/archlinux-patches

Add Linux Arch environment and host packages
Merge pull request #178 from hashdist/ahmadia/add_mpi4py

add mpi4py from March 2014